Q.In My Home One Jackfruit Tree It Has 8 Years Age Still It Not Getting Fruits. Why
It’s height nearly 20 feet it’s in damp condition.

Certified GKH Gardening Expert
You can keep it pruned to about 15 feet to make harvesting easier. Also, since it isn't producing, I'm wondering if you are fertilizing. Besides nitrogen, phosphorous and potassium, your tree needs magnesium.
The damp condition may be preventing the fruit. Jackfruit trees do not like wet feet.
Here is more info:
https://www.gardeningknowhow.com/edible/fruits/jackfruit-trees/growing-jackfruit-trees.htm
https://www.hort.purdue.edu/newcrop/morton/jackfruit_ars.html