What did Jacob vow to give God at Bethel if God kept him safe?

Answer: A tenth of everything

Jacob vowed that if God watched over him, the LORD would be his God, and of all God gave him he would give a tenth.

“And this stone I have set up as a pillar will be God’s house, and of all that You give me I will surely give You a tenth.””— Genesis 28:22 (BSB)