John 6:28-29

Then they asked him, "What must we do to do the works God requires?" Jesus answered,  "The work of God is this: to believe in the one he has sent." 

What must we do to do the works God requires?
Ephesians 2:8-9  For it is by grace you have been saved, through faith--and this is not from yourselves, it is the gift of God--not by works, so that no one can boast.
Titus 3:4-7  But when the kindness and love of God our Savior appeared, he saved us, not because of righteous things we had done, but because of his mercy. He saved us through the washing of rebirth and renewal by the Holy Spirit, whom he poured out on us generously through Jesus Christ our Savior, so that, having been justified by his grace, we might become heirs having the hope of eternal life.

The work of God is this: to believe 
1 John 3:23  And this is his command: to believe in the name of his Son, Jesus Christ, and to love one another as he commanded us.

in the one he has sent 
John 6:57  "Just as the living Father sent me and I live because of the Father, so the one who feeds on me will live because of me."
John 10:36  "... what about the one whom the Father set apart as his very own and sent into the world? Why then do you accuse me of blasphemy because I said, 'I am God's Son'?"
John 11:42  "I knew that you always hear me, but I said this for the benefit of the people standing here, that they may believe that you sent me."
John 17:20-21  "My prayer is not for them alone. I pray also for those who will believe in me through their message, that all of them may be one, Father, just as you are in me and I am in you. May they also be in us so that the world will believe that you have sent me."

Scriptures taken from the Holy Bible, New International Version® NIV®, 
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