Answer:
B. The speaker felt his knees shaking. However, no one in the audience even knew he was nervous.
Step-by-step explanation:
An omniscient narrator knows everything that happens before the story, during the story, after the story. The key pointer is the narrator knows every character's thoughts and feelings.
A. Vicente learned that opening a candy shop would be no easy task,
but that wouldn't stop him.
The narrator is only discussing Vicente's thoughts, so this could be first-person narration.
B. The speaker felt his knees shaking. However, no one in the
audience even knew he was nervous.
The narrator talks about the thoughts of both "the speaker" and the audience, so the narrator is omniscient.
C. "Stop, thief!" the guard shouted, but the thief was too quick and
made it over the castle walls.
This could be any third-person objective or limited narration. It's like similar to watching a movie; you aren't told what the characters are thinking.
D. Ting looked across the table and noticed the frown on her date's
face. Something must be wrong.
This could be first-person narration since we only know the thoughts for one character, Ting.