"Hvaserdu?"

They're taking the hobbits to Isengard!

That would be the translation of "Hva ser du på?".

To me it comes off as sloppy language at best, and confusing at worst.
It requires a lot of context to make sense, and thus would not work in this sentence.

Settings where it's passable to omit the "på" from "se på":

"Hun ser aldri (på) nyheter."
"She never watches the news."

"Han sovner alltid når han ser (på) TV."
"He always falls a sleep when watching TV."

In both cases it's no longer a description of a single occurrence, but treated more like a phrasal verb describing a habitual action. And the second example still grates me a little. ;)

Bottom line: You're safer to avoid it, especially in writing.