At the beginning of the novel Stephen is sensitive, intelligent, and pious. He seems destined for a life in the church. It isn't until much later in the novel that other characteristics such as artistry, sensuality, and curiostiy appear and indicate his tranformation and pull toward the life of an artist.
Characterization is a literary process where the author uses several techniques to make characters seem real, believable, sympathetic, and vivid to the reader. When your teacher is asking you to identify characteristics, he/she is asking you to imagine the character is a real person and then identify what particular actions or words help identify or typify the character. For example, if Dedalus is viewed as pious, there must be something he has done or said that made other characters in the book believe that about him.
In order to identify character traits look at the characters actions, thoughts, and conversations. Also, look at what other characters say about him, and try to identify why the character is viewed that way by others.