On which mountain did Barak gather his 10,000 men before attacking Sisera?

Answer: Mount Tabor

Deborah told Barak to march to Mount Tabor with men of Naphtali and Zebulun; he came down from there to rout Sisera.

“She summoned Barak son of Abinoam from Kedesh in Naphtali and said to him, “Surely the LORD, the God of Israel, is commanding you: ‘Go and march to Mount Tabor, taking with you ten thousand men of Naphtali and Zebulun.”— Judges 4:6 (BSB)