Just a few would be that
1) Kennedy was shot from the front
2) The rifle which Oswald allegedly used was not only low quality but the scope was drastically misaligned.
3) One of the witnesses to see a man fleeing the scene of the Tippit murder stated that the man was not Oswald. After being shot in the head and recovering he changed his tune and said that Oswald was the man he had seen.
4) The time frame does not allow for Oswald to leisurely leave his house and shoot Tippit at the time alleged.
5) Oswald was supposedly arrested at the theater with a revolver yet the shells recovered from the Tippit murder scene were from an automatic pistol.
6) Policemen ran up to the grassy knoll only to be met by men with Secret Service badges turning them away. But there were no Secret Service agents in that area.
7) There is a rather long list of witnesses who died violently or in other suspicious circumstances.
8) The paraffin test given to LHO indicates that he had not fired a rifle that day.
9) The time between the shooting of the President and the point at which Truly and Baker confronted a calm and not out of breath LHO on the 2nd floor of the book depository was only 72 seconds-not at all enough time for LHO to have done what he was alleged to have done.

and so on...