Two days ago, I bought Christmas gifts ,but forgot to ask for gift receipts. Can I go back ask for one?

Just save the receipt and don't worry about it. Just offer to give them the receipt you got when you purchased it if they want to exchange or return it. I have never heard of purchasing something and then getting a "gift receipt" in case someone doesn't like it.

Depends on the store. At the store I work for you must do gift receipts during the transition. I can look up your original receipts and print them. But the register will not allow me to print a gift receipt if it was not in the original transaction. 

You can return all gifts, and then repurchase and get gift receipts. 

Each store will have different policies and abilities.  Call and ask

Yes you can                     

no, that is a hassle. 

The only way to find out is to try.

you could try doing that

If you used a credit card the clerk can use it to return the purchase to that card.

It can't hurt to try. If they can't do it, ask them to refund the items and sell them to you again.