I really struggled to answer it. Not because I am not joyful, but because in context I thought the question actually meant, "What makes you happy?"
Those are vastly different questions!
My happiness depends on external factors.
Did someone spill the whole gallon of milk? -Unhappy. Mad. Grouchy for the next hour.
I got a card in the mail instead of bills?- Happy. I'll even re-read it several times that day.
Back talk?- Angry. And a spanking!
Obedience?- Totally happy!
You can affect my level of happiness. You can even take it away completely by your actions.
No one, no where, at no time, by no means can take away my joy.
My joy comes from who I am in Christ.
The Bible tells me that I am a joint heir with Jesus. I will inherit His full inheritance from His Father because God is also my Father, too.
"The Spirit Himself bears witness with our spirit that we are children of God, and if Children, then heirs- heirs of God and Joint Heirs with Christ, if indeed we suffer with Him, that we may also be glorified together." Romans 8:16-17 New International Version.
The Bible tells me that I can go to God and cry out Abba to him. I can call God my daddy! God is not some far off deity that cannot be approached. He is my DADDY. He longs to spend time with me, to answer my questions, to scoop me up when I have fallen down, to heal my hurts and to rejoice in my triumphs- like any other daddy in the world.
"And because you really are His sons, God has sent the Holy Spirit of His Son into our hearts crying Abba (Father)!" Galatians 4:6 Amplified Version
The Bible tells me that even though I may suffer persecution, the Spirit of God rests on me and , ultimately, He will be glorified.
"Beloved, do not think it strange concerning the fiery trial which is to try you, as though some strange thing happened to you; but rejoice to the extent that you partake of Christ's sufferings, that when His glory is revealed, you may also be glad with exceeding joy. If you are reproached for the name of Christ, blessed are you, for the spirit of glory and of God rests upon you. On their part he is blasphemed, but on your part he is glorified. Peter 4:12-14 New King James Version
No one can take my joy away from me, because my joy comes from being secure in my salvation. Being secure in my Heavenly Father. Knowing fully that Jesus loved me enough to pay for my sins through His death so that I may share in His inheritance.
What brings you joy?