"Cosa ti potrei dare?" means "What could I give [to] you?" or (hope I'm right :-ʃ ) "Mit neked adhatok?". "Cosa potrei dare?" makes no sense, unless there was a previous sentence that clarifies who is the receiver, but usually there is always an indirect object, even only a pronoun:
"Cosa ti potrei dare?" / "Cosa potrei darti?" (neked)
"Cosa gli potrei dare?" / "Cosa potrei dargli?" (to him)
"Cosa le potrei dare?" / "Cosa potrei darle?" (to her)
"Cosa vi potrei dare?" / "Cosa potrei darvl?" (nektek)
"Cosa mi potresti dare?" / "Cosa potresti darmi?" (te - nekem)
...
You can see that you can put the clitic (unstressed) pronoun before the modal verb as well as linked after the infinitive.
Here, "cosa" is an interrogative pronoun and it is invariable; incidentally "cosa/-e" is also a noun that means "thing", "stuff".