Great thinking skills / smart (not academic) lead

I don't want a lead who just get high grades, I want to see the thought process of the character/s

Not necessarily detective drama, Cheese in the Trap (just the webtoon) leads are smart and we can see the way they think through things

• Galileo
• Liar Game
• Unnatural
• 99.9 Criminal Lawyer
• Maou
• Mad Dog
• 38 Task Force
• The Player

Currently airing dramas with smart leads:

• The Crowned Clown 
• The Last Empress 

Completed dramas with smart leads:

• A Beautiful Mind | Smart ML and 2ML.
• Children of Nobody | Both.
• Cruel City | Smart ML and 2ML (as well as other support characters and antagonists).
• Feel Good To Die | Both. This one is lighthearted, though.
• Gu Family Book | Both. Street smarts.
• King2Hearts | Both, but the FL starts questionable.
• +1 to Lawless Attorney | Both.
• Mask | Smart FL.
• Mother | Smart FLs.
• Pinocchio | Both.
• Suspicious Partner | Smart ML.
• Terius Behind Me | Both. This one is also lighthearted.
• The Ghost Detective | Both. Though the ML is a bit more active.
• The Guest | Smart ML, 2ML and FL.
• Voice | Both.
• Voice 2 | Both and smart antagonist.
• While You Were Sleeping | Smart ML, 2ML and FL.
• You're All Surrounded | Smart ML (academic), 2ML (instinct) and FL (resourceful).

I would recommend 

• Guardian (The main lead is Chief of a Special Investigation Unit and has to solve cases while looking for ancient objects that also the villains want to get, so he's smart and good at combining hints and leads)
• Time Slip Dr. Jin (Korean Remake of the Japanese Parent Story JIN) (The main character is a doctor who travels back in time and has to find smart ways to treat patients with his limited options) 
• Detective L (the trailer makes the main lead look like Sherlock Holmes with the typical analytic thinking, so you might want to check it out) 
• The Lost Tomb Series (similar to Indiana Jones; treasure hunters adventure series, they have to solve puzzles to find what they're looking for) 

Hope that helps. :)

 Fairplay:

Thanks, but may I ask smart in what way? Will I see decent thought process of the leads? Deductive skills, critical thinking, clever, how they analyze events, strategy, reasoning, etc.

Sure, not a problem. I'll elaborate on my answer as best I can. Keep in mind that these are all judged based on Korean standards. If you are looking for western series as well, I can recommend some that would blow some of these out of the water in terms of critical thinking and character deduction skills.

Currently airing dramas with smart leads:

• The Crowned Clown | The ML shows leadership qualities. He's able to inspire people to follow him as he makes decisions that benefit all the people, not just those in power. FL is also shown sharp wit in navigating palace politics.
• The Last Empress | You have various characters vying for power within the palace. Some are able to manipulate others while others are capable of observing, learning and acting based on the information they have collected. Oh Sunny (the FL) stands out because we see an evolution of her character. From the typical weak but kind protagonist, she shows that she' not only capable of adapting to her circumstances, but she also has the courage to walk into a monsters' den and make an impact.

Completed dramas with smart leads:

• A Beautiful Mind | If you've checked the premise of the show, you know the ML is a doctor who is actually a psychopath (unable to feel any emotion). So his father (in an attempt to give him a decent life) instructed him on how to read emotions. Which means you get a lot of his thought process based on logic and what he's learned as the show progresses. It reminded me slightly of "Sherlock Holmes" in a way.
• Children of Nobody | You get a FL who's a child psychologist, so her contribution is in regards to the thought process of the vigilante they are after. The ML is a detective, but he contributes more in giving the FL advice on a mystery that involves her. This show does focus more on the vigilante's motivations (which are interesting in and of themselves).
• Cruel City | If you've seen the American movie "The Departed" then this one follows along those lines and expand upon it. The ML is an undercover cop who's immersed himself in a drug war. You get characters that excel at streets smarts trying to topple cruel giants. As the story unfolds, alliances shifts and break as characters try to find ways to survive, outlive and outlast their competitions.
• Feel Good To Die | This is a show which excels at character development. You get characters who are given moments of reflection that allows them to change for the better. The ML is the one who changes the most, with the FL simply finding the courage to stand up for her beliefs.
• Gu Family Book | The ML is a character who doesn't consider himself smart, yet can come up with strategies based on wit alone. The FL is emotionally intelligent, which allows her to deescalate problems and simplify situations. On top of that, you get the antagonist and the admiral, both of whom show great levels of strategizing when fighting for power.
• King2Hearts | ML starts out as a party boy/jerk but due to his circumstances, ends up having to understand and play the politics of his country. This one doesn't show that much level of critical thinking, but he does play a few moves on the antagonist. The FL is also shown to think of her feet when the situation demands it.
• +1 to Lawless Attorney | Both characters show a level of emotional intelligence throughout the drama. They are also good at adapting to situations and outmaneuvering their enemies. They even go to the extent of forging alliances with some of their enemies in order to topple the "final boss".
• Mask | The FL is forced to impersonate a woman who looks like her by the 2ML, who has a grudge against the ML and his family. Halfway through the show, however, the FL decides that's not going to work and goes toe to toe against the 2ML.
• Mother | Both characters show a remarkable level of emotional intelligence (the little girl even more). Through heart to heart conversations, we also get to see some of their thought processes. Even the antagonist's motivations are well executed and explained.
• Pinocchio | This show deals with the fallout of running a story without checking all the facts. The ML ends up learning how a false narrative can change and ruin the lives of other people. While the FL is faced with a decision whether to be true to her sense of righteousness or ignore things to save her career.
• Suspicious Partner | The ML is a prosecutor (later a lawyer) and, as he tackles some cases, we see his thought process when it comes to assembling all the pieces of a puzzle together.
• Terius Behind Me | FL shows a remarkable level of common sense, critical thinking, and wit.
• The Ghost Detective | ML is a detective, so we get to see some of his deducting skills in play. The antagonist's motivations also show a clear sense of purpose which are explained in a clear and reasonable way.
• The Guest | The three leads show deductive skills and some critical thinking.
• Voice | You get everything. Deducting & observation skills, clear thought processes, event analysis, strategies and leadership qualities (this last is especially true for the FL).
• Voice 2 | Same as above.
• While You Were Sleeping | Critical thinking.
• You're All Surrounded | Smart ML (academic), 2ML (instinct) and FL (resourcefulness).

Nirvana in Fire.. 9.1/10 rating here, one of the best historical dramas I have watched. The main lead secretly assists his friend Xiao Jingyan, the unfavoured son of Emperor Wu and wisely rids the court of all scheming officials. From what I recall he was very smart and his schemes were very well thought out.

Tysm :) @3GGG 

Thank you @OldAnimeLady @Stevie70 @fanitha :)

• +1 Mad Dog
• Hello Monster
• The Story of Ming Lan
• The Story of Yangxi Palace
• The Princess Wei Young
• Love O2O
• Misty

All of these have main characters that are excellent at strategizing (predicting moves, making moves, and taking countermeasures) and in most of them at least one main character is shown (not simply described) to be brilliant in their field (e.g. politics / public policy, business, computer science and gaming, journalism, etc.).