You'll be disappointed even if you do find a handwriting app; the NT, NC and a lot of other tablets use capacitive touchscreens which do not support the precision needed for handwriting. In order to take notes, you really need a device with a digitizer screen, and at this moment I'm at a loss to suggest one...
There is a pen, I think it is called LightScribe, which stores everything you write inside it then you just plug it into your computer and upload all your notes. You can alway put them on your Nook for reading. Not the same as writing on the Nook but maybe close. I personally have never used the pen but i've always wanted one and it has great reviews.
There is a new app available called Write Notes,
says you can do handwritten notes using your finger.
I have not used it yet and I am new to Nook tablet but you can check.