Student or Learner
Both 1 and 2 got 1 million hits respectively:
1) I am good for nothing.
2) I am a good for nothing.
I would expect to see the noun hyphenated: I am a good-for-nothing.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
Tip for a better title: I am good for nothing.