If you're talking about the diagonal partial-moon-shaped bright white area... that looks like separation to me. Closed down two to three stops you can still use the lens. However, the separation will probably get worse.
I dunno, I see rainbowing along the whole element which may indicate that the separation is wider than that one section where it has totally separated, or where the glue is damaged.
Don't usually see that on the old Nikons. If you avoid temperature extremes it may remain stable for quite a while. Probably won't affect your images, being out on the edge like that. If it does, it will be when it's wide open.
I've had the old finger smudge spoil photos too. Thought I had a bad lens, when all it needed was wiping off the rear element.
One of the sharpest lenses by dad used (and he had multiple copies of this lens) was a 53 4.5 Biogon that had been dropped with a straight crack in the rear element group
I have a 35/2 Nikkor-O that, under the right conditions, displays Newton's rings where something near the middle is separating. I can't see any effects in the photos, though. I presume it will eventually need a recementing job done, but for now I just use it - it's a tossup which I use more, 35 or 50 on the Nikons.