When to prune a dephne?

I assume you mean Daphne and it should not be pruned... it should be pulled out. The Daphne is an invasive weed and has extremely toxic blueberry-like berries. I once brought a Daphne home from the woods to have as a houseplant because of it's beautiful foliage. Once I found out that it was toxic I destroyed it. If you have an abundance of Daphne you can get a tool called a Pullerbear to pull it out of the ground by it's roots. Hope this helps!