both of two are formal expression and polite way used in when you talk with older people or meeting with someone first time. ( No one want to friendy speak in first time. I think it is rude manner) but 잘 지내십니까? is more polite and likely used in official place. and 잘 지내시나요? is also polite, but lf you want to make closed relationship with whom, 잘 지내요? is more recommended expression in korea I think.

Yes, both mean the same thing but different in speech style. "잘 지내십니까" is more formal. \^o^/

Check this video; https://youtu.be/aG0TMm8aWkQ