When is the best time to trim knock out roses?

Late winter or early spring are the best times. Click on the article below to read more. Wishing you the best.

https://www.wikihow.com/Prune-Knockout-Roses

before the new growth starts to emerge

You should cut back the flowers after they bloom; I just use this to keep the bushes from over-running the area! Actually, I think with knock-outs you can trim back any time. If you are in an area with harsh winter, they are probably not blooming now, so you can cut them back as much as you want. We are in North Texas and they bloom nearly all year round!

They bloom almost all year here also and I just prune them back whenever they get too out of shape.

Prune the roses after the buds break dormancy. The major pruning period for knockout roses is in late winter to early spring, just as the bush begins to break out of its dormancy stage. Check for bud formation on the stems of the plant

I would do it as soon as the frost is over. Next year, prune before the first frost.

Right after the flowers come.