Yes, you can eat dragon fruit stems, but you have to select the young one.
I fry it with egg.
Eat it with sea weed.
Eat it with rice paper
Most of everyone that grows dragon fruit would eat the fruit and discard the young stems. However, the young stems can be eaten like cactus paddles. It has similar flavor, sour and slimy texture. Try to eat only the young stem that is about 10 inches or shorter. When it gets longer, the stem is a bit tougher than usual. Dragon fruit stems have less cactus thorn than the paddle. If you get stab, it's still hurt the same.
When you use cheese instead of egg, use sweet cheese to balance the sour flavor of the cactus. That was the reason, I cook with oyster sauce. You can still add dried red peppers with the cheese. Again, make sure to use sweet cheese. It'll taste better.
I also use the young stem for my sweet and sour soup and stir fried vegetable. Sometimes, I even make juice out of it.
If you would like to learn how to cook it, watch my YouTube. The link is below. Thank you.
www.youtube.com/watch?v=1dnwGQ2N28I