Who urged Belshazzar to summon Daniel to interpret the writing on the wall?

Answer: The queen

Hearing the outcry, the queen entered the banquet hall and reminded the king of Daniel, whom Nebuchadnezzar had made chief of the magicians.

“Hearing the outcry of the king and his nobles, the queen entered the banquet hall. “O king, may you live forever!” she said. “Do not let your thoughts terrify you, or your face grow pale.”— Daniel 5:10 (BSB)