잘있는거지?
Recently I heard this in a drama, and I was wondering if it was a way of saying "are you doing well? "
Because I haven't heard it before I had a lot of trouble figuring out how it could have been spelled, but I came to this. Please help me.

Question

잘있는거지?
Recently I heard this in a drama,  and I was wondering if it was a way of saying "are you doing well? " 
Because I haven't heard it before I had a lot of trouble figuring out how it could have been spelled,  but I came to this.  Please help me.

Answer

Yeap, the meaning is correct.

To be specific, when we say to someone "잘 있는거지?", we haven't met each other for a while. 
Also, we don't say that phrase in person. we only say it through phone, e-mail, text... etc.