how is the passenger side mirror held on, on a 96 legacy.

it's loose and wanted to tighten it.

If there is a triangular shaped piece at the inside of the door from the mirror, gently pry it loose and you'll find a few nuts behind that should tighten it up. The triangular piece has three small plastic wings that can be broken if you just tear into it.

it has a little speaker behind the mirror. how would this come off.

Use a small screwdriver to gently pry off the speaker grill and you should then see the actual speaker being held on by the same nuts that hold the mirror to the outside.