Yes. You can eat milk thistle.
The milk thistle is edible as long as you remove the very sharp leaf-spines first.
You can eat milk thistle including the young stalks, leaves, roots and flowers of the milk thistle which are all edible.
Milk thistle and the young stalks, leaves, roots and flowers can be eaten raw or cooked.
If you don't remove the sharp leaf spines it can cut your throat which can be deadly.
So as long as you remove the sharp leaf spines from the milk thistle first the rest of the milk thistle is edible both cooked or raw.
I prefer to eat milk thistle cooked.