As ADC, how do you catch Trist?

In Lane or after mid game?

In Lane, your only chance really is to have the support land some initiation, and follow it up if you can. E.g. a Morgana bind followed by jinx chompers under her. Otherwise, just wait for her to burn the jump and then abuse the cooldown if she comes back. Ganks can work if she pushes far enough, which she will due to her e passive.

Mid game, you are best off having someone come in from behind if possible. Unless you have an amazing chaser.