I need drama recommendations where a naive & sweet male lead gets manipulated and made to work by manipulative & cunning female lead. 

The ones I've watched so far are :

DoS Deka

The Confidence man JP

Miss Devil

Doctor X (all seasons)(Some episodes)

Legal V (Ongoing)

(No specific genre/language preference)

They may not be exactly what you are looking for, but the ones I can relate with naive ML and smart FL:

Ho Go's love - She's famous athlete and have strong personality while he's a good for nothing.

Divorce Lawyer in Love - BossFL- employerML relationship she's a jerk sometimes.

Material Queen - Gold-digger FL and poor naive ML.

The Happy Loner - Selfish and lonier FL and extroverted ML

Dream High - She plays with him all the time and he, a countryside boy, likes her.

Idk if I'd call Ta Hwan "sweet", but Empress Ki

Across the ocean to see you