Does the new part of the nail need to be washed after trimming it during ghusl al-janabah, or is the first washing before trimming sufficient?

There is no need to wash a clipped nail. However, the entire body must be washed during ghusl (ritual bath), including the nails and the skin beneath them. Some scholars view minor dirt beneath the nail as excusable. If nails are clipped after they have been washed, there is no need to rewash the remaining parts. Clipping nails during ghusl is not a Sunnah (prophetic tradition) and does not invalidate the ghusl, as continuity (muwalat) is not a condition for it according to the majority of scholars.