Q.When Do You Prune Fruit Trees
I HAVE A CHERRY TREE WHICH HAS GROWN WELL BUT NO FRUIT APPLE TREE WHICH HAS ONLY PRODUCED SMALL FRUIT CONFERENCE PEAR WHICH ONLY PRODUCED TWO PEARS AND A PLUM TREE WHICH HAS PRODUCED QUITE A LOT OF FRUIT BUT A LOT OF IT WAS SCARRED.

Certified GKH Gardening Expert
These trees will have different pruning times. Here are some articles that will help you to know when is the best time to do so for each:
https://www.gardeningknowhow.com/edible/fruits/cherry/cherry-tree-pruning.htm
https://www.gardeningknowhow.com/edible/fruits/apples/pruning-apple-trees.htm
https://www.gardeningknowhow.com/edible/fruits/pear/pear-tree-pruning.htm
https://www.gardeningknowhow.com/edible/fruits/plum/plum-tree-pruning.htm