Hey, I met Dorn Il-Khan and I switch Imoen with him because there is 6 party member, she leave from my team, but I want her back. Where is she? Where I can change commpanions in game? There are waiting somewhere or leave permanently? I was looking in Friendly Arm Inn. But only Neera is here.
Any help??

She should be somewhere near the place where you left her. Try to search for her there.

In BG: Imoen should always be where you leave her.
In BG2: Imoen should be in the Copper Coronet.

Generally: in BG, companions may stay where you leave them or leave you permanently depending on whether they hate you or not. If your reputation contrasts too much with their alignment, they will leave you (except Imoen).

the Dorn map is south of the Nashkel town... heading toward the Mine

it is a bad idea to leave people in special maps but you are playing BGEE so if you run back and forth between those areas it should come up again and you can ask Imoen to rejoin