Centre Game - 1. e4 e5 2. d4 Qe7 - What's the theory

just taking on e5 is good enough. black doesn't benefit from placing the queen on e7 if he opens up the position as then his kingside is clogged, so he should keep it closed.
Early queen moves are generally bad: the queen can be chased. It is genarally best to play 2 pawns first, then 2 knights, then 2 bishops, then castle and last but not least move the queen. On e7 the queen obstructs the diagonal of Bf8 and thus hinders castling O-O.

just taking on e5 is good enough. black doesn't benefit from placing the queen on e7 if he opens up the position as then his kingside is clogged, so he should keep it closed.
This is perfect thank you

Theory rarely analyzes "stupid" / nonsense moves.
Just general principles : develop with white, don't bother about gambiting pawn, black will lose tempi and u will get a very nice position.
So 3.dxe5 or 3.Nc3/Nf3 are all fine.
Have a look on this article :
https://www.chess.com/article/view/how-to-deal-with-outrageous-openings

Qe7 slows black's development of the kingside. Focus on fast development and castling and you'll automatically have a nice position.
A common beginner mistake is to try to punish a poor move immediately by attacking. If you do that then you wont be able to take advantage of the defects of 2...Qe7

There is a reason you dont see this move at the top level of play. But for the other 99% of us? Im sure its playable.

When dealing with a move like 2... Qe7, ask yourself: Under what conditions is this move good? And under what conditions is it bad? Then arrange the conditions to make it turn out bad!
As white, my immediate instinct would be to close the center with 3. d5. The queen on e7 might make sense if the e-file opens, but if the e-file stays closed, then Qe7 just looks misplaced and stupid.
- How does black develop the DSB? Either the queen has to move again (and none of its squares look great), or the bishop has to develop via g7, which doesn't make much sense when the long diagonal is blocked for the foreseeable future.
- Where will black's b8 knight go? It's denied the natural c6 square. To put it on d7, black has to push the pawn to d6, which makes the DSB (and queen) even more passive.
- Black's LSB isn't looking so good either. Where does it belong?
- How is black planning to castle? It could be a long time before black disentangles enough to castle on either side.
No, white isn't yet winning after 3. d5. There's a lot of chess left to play, but black does have some real problems to solve. White has basically gotten a comfortable space advantage for free, since black's Qe7 probably wasted two tempi.