"Can I have a drag?" - What does that mean?
SCRIPT
John: "Hmm. Hey, can I have a drag?"
Gabrielle: "Absolutely not. You're much too young to smoke."

QUESTION
Drag - A slang of "doing smoke?"

Question

"Can I have a drag?" -> What does that mean?
SCRIPT
John: "Hmm. Hey, can I have a drag?" 
Gabrielle: "Absolutely not. You're much too young to smoke."

QUESTION
Drag -> A slang of "doing smoke?"

Answer

We don't say doing smoke, it's always just smoking. A drag means a puff ( to inhale a cigarette) other words you might hear are, a toke, a pull.

Answer

Here a drag means a puff on his cigarette.