Guess I'm stuck in car? (8)
I believe the answer is:
estimate
'guess' is the definition.
(I know that guess can be written as estimate)
'i'm stuck in car?' is the wordplay.
'stuck in' indicates putting letters inside.
'car?' becomes 'estate' (type of car).
'im' placed inside 'estate' is 'ESTIMATE'.
(Other definitions for estimate that I've seen before include "Calculate roughly" , "Judge the worth of" , "Judgment, appraisal" , "rough judgment" , "Reckon, guess" .)