drawing app resolution/dpi nexus 7 (markers app)

Just curious, do you use any sort of stylus?
For printing on a standard size paper, it should be fine. Meaning the screen has enough pixel density so the image doesn't have to be blown up, I think. But mind you, you're drawing on a 7 inch screen and an A4 is significantly larger. So it might not look as good in a bigger size. If you zoom in while drawing you could have a much more detailed image.

In any case, the screen density is like 210+ ppi and I think 240 dpi, which should well be enough for printing.