It's the first-person singular form of the verb "rozumieć" (to understand) in the negative.
Here are some examples of how it can be used:
* Nie rozumie tego, co mówisz. (I don't understand what you're saying.)
* Przepraszam, nie rozumie. (Sorry, I don't understand.)
* Czy możesz to powtórzyć? Nie rozumie. (Can you repeat that? I don't understand.)