If nodular melanoma was picked off. would a biopsy of the underlying tissue a few months later still be accurate to make a diagnosis.

Possibly: Depending on the depth the melanoma, a biopsy of the area could detect abnormal cells. Best to see a dermatologist as soon as possible.

??: Melanoma is a skin cancer that penetrates into the skin. It will not be able to be 'picked off'. See your doctor to see if a biopsy is needed.

Yes: Even though it might look like it was completely picked off, you can still have residual melanoma in the same spot. You absolutely need to have not just a biopsy, but an excision of the skin area to decrease the chance of the melanoma growing back. Depending on how deep the melanoma is/was, you may also need to have a few lymph nodes removed to make sure the cancer hasn't spread.