Complex sentence: Trinneer didn't know what to expect from the part, as during the audition he had only the seven pages of script to base his performance from as he was only told that the character originated from the Southern United States.
Split into simpler sentences: Trinneer didn't know what to expect from the part. During the audition, he had only seven pages of a script on which to base his performance, and was told only that the character originated from the southern United States.