Pub's motto, questionably — this? (7,2)
I believe the answer is:
Here is my best explanation:
'this?' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'pub's motto questionably' is the wordplay.
'questionably' is an anagram indicator (questionably can mean strange).
'pubsmotto' is an anagram of 'BOTTOMS UP'.
(Other definitions for bottoms up that I've seen before include "Down the hatch!", "cheers", "Your good health!", "Toast", "Cheers!" and "down it goes!".)