How do I view messages in trash?

What sort of messages?

Mail? If you have Time Machine running, open that with the Mail app foremost. You can recover most deleted messages there.

As for Apple Messages, there’s no good way to do that:

How to Recover Deleted Messages in the Apple Messages app - Apple Community

That’s written for iPhone and iPad and not Mac, but the iCloud setting still holds, and I’ve not tried a Time Machine recovery with Messages app foremost for not-iCloud-enabled configurations, and would not suggest trying a Time Machine restore to recover a deleted not-iCloud-enabled message.

sharig40 wrote:

I just want to see what email is in the TRASH. I accidentally deleted my archive folder

It’s either in the deleted messages folder, or it’s in the Time Machine archives. Your mail provider might have deeper backups.

Delete emails in Mail on Mac - Apple Support (includes how to view deleted mail messages)

One of the very few ways to indicate that data has value is with Time Machine backups or some other scheduled onsite or offsite backup. Otherwise, that data is one mistake/error/loss/theft/dunking away from loss.

If you mean messages from the Messages App & not eMail messages, as far as I know they're gone for good unless you might have a Time Machine backup of them.

Log in to your WebMail in a Browser& see if they are there still somewhere.