What can be done if I am being sued for a car I traded for 2 years ago being involved in an accident?

If you notified the DMV of the change of ownership, they would have that on record. It seems you did not. So you need to tell the DA [appears that you are being charged with a crime for the accident] how they can find the new owner and provide as having people who know you sold the car or who have not seen the car in your possession for at least a year present sworn affidavits [I, ?[name].., declare under penalty of perjury and the laws of the State of California as follows at end put I,..., declare under penalty of perjury that the above is true and correct as to my own knowledge and belief, and if on belief i believe it to be true, and that is called as a witness I could and would so competently testify].