Hi and welcome on the last but pretty lively and active server
To answer your questions:
1. Now my question is whats the best solo class is to farm elga/paris etc.
Paris can be done with any class if you play right. For elga (as said as it is to say) the x-spammer classes (Invoker, Earth Master, Destroyer) have the advantage.
2.My favourite class was the sentinel how is he on the end game?
Unfortunately, the damage of the sentinel has been nerfed drastically. So Sentinel is the weakest PVE class by now in terms of damage. For PVP he's still good as long as you have high movement speed and element weapon.
3. can i play him (Sentinel) for doing solo runs etc or is he not so good ?
As said above, Sentinel is probably the weakest PVE class right now. For doing solo runs or F1 farm I would recommend one of the other classes
4. What is the best or which classes can do everything solo?
If you wanna do everything solo, you might want to go for an x-spammer. However, if you want not only to solo dungeons but also want to be successful in F1 farm, I'd recommend Destroyer which I call a "hybrid" due to his ability to clear missions/dungeons with x-spam but also with skill only (for Rank).
Nevertheless, I would recommend to stick to the classes you like and not to those which promise the most success (because "weaker" classes can also be succesful in their very own way)