In the closing doxology of Jude, who is able to keep you from stumbling?

Answer: God

Jude closes with praise to Him who is able to keep you from stumbling (KJV: falling): the only God our Savior, through Jesus Christ.

“Now to Him who is able to keep you from stumbling and to present you unblemished in His glorious presence, with great joy— to the only God our Savior be glory, majesty, dominion, and authority through Jesus Christ our Lord before all time, and now, and for all eternity. Amen.”— Jude 1:24-25 (BSB)