Most charities that you donate your car too will require you to have the title to transfer ownership to them.
The charity will usually fix the car and sell or it sell it off to someone else who then requires the title to register it in their name and drive it.
If the car is truly junk then you might be able to donate the car to the charity as junk or parts and write out a bill of sale that you get from the DMV or courthouse.
I was able to donate an old junker car that was my grandmas who died to a charity by filling out a bill of sale and they accepted it that way.
But not all charities you donate your car too will accept the car without a title because they may be weary that you don't actually own the car.
If you do donate your car without the title then your tax write off won't be as good as it would be if you do have the title.
If you own the car and it's in your name and you lost the title to the car you can go to the DMV and get a new duplicate title.
Just tell them you lost the title and then bring the required paperwork in and they can mail you a new title to the vehicle.