Q.wintering mandevilla outdoors
what should i do after pruning if i keep it outdoors in winter? what do i cover it with?

Mulching over the roots and protecting the top portion will help your plant survive the winter. You can cover the top with a tent of burlap, plastic, or other fabric.
https://www.gardeningknowhow.com/garden-how-to/mulch/mulching-plants-in-winter.htm
If you live in a colder climate, see this article:
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/winterizing-mandevillas.htm