If the title to the car says and/or then only one person needs to be present to sign the title over to the new owner.
But if it says just and between the names then both parties will need to sign the title to transfer ownership but both parties don't have to be present at the time you have the title signed and notarized.
The other party that owns the car along with you can sign the title later but they must sign the title if two parties own the car and it says and between each name such as Jane and Doe.
If it says Jane and/or Doe then only one person needs to sign the title.
Of course those Jane and Doe would be your own names on the title. lol