Can you use Mawile GX's "Captivating Wink" Ability if your opponent's Bench is full?
No. It's public knowledge that you can't put down any additional Basic Pokemon on your opponent's Bench, so you cannot use the Ability.
Source: Unified Minds FAQ (2019-07-19), TPCi Rules Team (2019-08-01)

Relevant cards

Note: All applicable cards may not be listed below.
SM11_141
SM11_141
SM11_227
SM11_227
SM11_246
SM11_246