What did Solomon stand and kneel on to pray before the assembly at the temple's dedication?

Answer: A bronze platform

Solomon had a bronze platform built in the courtyard; he stood on it, knelt before all Israel, and spread out his hands toward heaven.

“Now Solomon had made a bronze platform five cubits long, five cubits wide, and three cubits high and had placed it in the middle of the courtyard. He stood on it, knelt down before the whole assembly of Israel, spread out his hands toward heaven,”— 2 Chronicles 6:13 (BSB)