What did Jeremiah see in his first vision, in Jeremiah 1:11?

Answer: An almond branch

Jeremiah saw a branch of an almond tree (KJV: "rod"); then he saw a boiling pot tilting from the north.

“And the word of the LORD came to me, asking, “Jeremiah, what do you see?” “I see a branch of an almond tree,” I replied.”— Jeremiah 1:11 (BSB)