This is the 5455th most frequent Korean word.
마셔
"마셔" means "drink" (imperative form in casual speech).
Here, '마셔' is used as the standard form of the verb 'to drink' in the present tense.
그는 물을 마셔.
He drinks water.
In this question, '마셔' denotes an action taking place in the immediate present, framed as a direct question.
너는 지금 뭘 마셔?
What are you drinking now?
Here, '마셔' is integrated into a suggestive phrase inviting someone to try the action of drinking.