If Titus is a tragic hero, he must have/do at least some of the following:
Noble Birth/Reputation. What information can you use to prove that Titus is an upper class citizen? What information can you use to prove that he is respected? You can find all of this information in the beginning of the play (Titus' return to Rome).
Pattern of Success. What information proves that Titus has been successful in his life? This information is available in the beginning of the play, too. Hint: Titus achieved much of his success while he was away from Rome.
Tragic Flaw. A tragic hero has a flaw that ultimately leads to his destruction. We see hints of Titus' tragic flaw early on (when he kills his own son for dishonoring him), and it becomes more apparent as he schemes to get revenge on Tamora and Saturninus.
Moment of Realization. Before a tragic hero dies or meets his downfall, he has an "Aha!" moment when he realizes what he has done wrong. Do you think Titus experiences this before he dies in the end of the play?
Pathos. A good tragic hero will make the audience feel pity, even if he is the one who gets himself in trouble. What reasons does the audience have to feel bad for Titus? Do we still pity/care about him by the end of the play?