if man quest in the mission log has finished and I not only abgebe when 2.0 is live, and I then abgebe I get experience points for it then
Not sure I quite followed but if you are asking if I have completed quests that I did before 2.0 and I turn them in after 2.0 will I get XP for them.
Again I can only answer that on PTS this was the case. I see no reason to believe this will not be the case. If I recall testing that some people had done with Character transfers, with XP boost got them 1.2 - 2 levels for a full set of Bel, Section X, and Ilum Dalies.
That being said, I don't expect the grind from 50 - 55 to be too painful. People will be running the new planetary quests and running things like EV HM for gear. I suspect most people will cap out at 55 before they finish new planet.