How did Jael kill Sisera, the commander of Jabin's army?

Answer: A tent peg through his temple

While Sisera slept from exhaustion in her tent, Jael drove a tent peg through his temple and into the ground.

“But as he lay sleeping from exhaustion, Heber’s wife Jael took a tent peg, grabbed a hammer, and went silently to Sisera. She drove the peg through his temple and into the ground, and he died.”— Judges 4:21 (BSB)