Didnt see a rules discussion area, so ill ask here.

1: Is a scene considered an encounter, or the full session, or somethng else? From how im reading it, i would say and encounter.

2: Can 1 medpac be used by one player to make a medcheck on themselves, avoiding the medcheck penalty, and then used on each other player in the group, in the same encounter? Or is it a once per encounter use?

1. A scene is usually considered an encounter or a reasonably short period of time.

2. A medpac is not a consumable item. A character can use it as often as desired, with a limit of the number of stimpacks contained. And if a character uses one on himself, then the penalty would still be present.

right but what im tryin to find out is can he use it on himself and then in the same encounter use it on another player?

I would say yes. The "scene" or "encounter" is the crew patching themselves up, dusting themselves down and getting ready for the next showdown (like the short scene between the trash compactor and starting the run to get back to the Falcon). If it happens too often, have guards come along, or droids, or mynocks, or something to keep them moving. An alarm or something similar would work too.

right but what im tryin to find out is can he use it on himself and then in the same encounter use it on another player?

This is allowed, yes.

According to the rules, a character can only receive a Medicine check once per encounter. There's nothing that says you can't try to perform a medicine check more than once as long as it is on different targets. You can also heal yourself, but the difficulty is upgraded by two.