Considering kissing priest's hand is a christianity learning, where did this learning came from?
Considering kissing priest's hand is a custom Where did this custom came from, Why it is wide spreading ? What is it's historical story ?
In Western Catholicism it is usually connected to the anointing of a newly ordained priest's hands with the Sacred Chrism. His hands have been set aside for God to do the Lord's work, and so some people (particularly in more traditional circles) kiss the hand. This is especially common with newly ordained priests, but also happens with priests in general sometimes.
There are many teachings about the Holy Kiss.
Romans 16:16 NKJV
2 Corinthians 13:12 NKJV
1 Thessalonians 5:26 NKJV
1 Peter 5:14 NKJV
If it is to kiss a hand or a ring or a sleeve or the air, I do not know. The tradition in the Catholic Church is the most likely example of the holy kiss. And if that example also flows out to kings of the past after the time of Christ, then that should be considered more evidence of its form. Here is a Reference you may enjoy.