Melted N-N-DMT freebase is pale-yellow at the lightest to yellowish-brown at the darkest, while DMT-n-oxide is brownish-brown and quite dark.
Apparently your friend could used zinc dust to convert to N-oxides back to freebase. SWIM's never done it though.
N-oxides (at least pure) are about 1/3 the strength of freebase when smoked (By SWIM's 2 tests) and about the same strength but about 1/3 to 1/4 as long when taken in pharmahuasca (SWIM's one test). Though SWIM never got any negative effects from it. Really N-oxides aren't too good compared to N-N-DMT, though there is a chance the goo is only slightly contain N-oxides and still be mostly N-N-DMT, goos can be a little harsh when smoked just because they are already melted so they vaporize REALLY fast.
There are 2 ways to go about testing whether it is N-oxide or freebase or a mix.
1:Redissolve it in naptha and recrystallize as usual, if there is a loss then it is likely the N-oxides.
2.Your friend could try smoking a measured amount SLOWLY and if there are aren't typically strong effects (N-oxides were unable to produce closed-eyed-visuals smoking ~35mg) then it is N-oxide (at least partly) If the effects are strong then it should be fine as long as there weren't any contaminants in the naptha.
Q21Q21's Tek: A comprehensive guide to extracting DMTThe 2 teks use non-toxic lime and vinegar and Tek 1: d-Limonene or Xylene or Tek 2: Naptha to produce very quick high yields with the greatest of ease.I am almost never on this site anymore so I will likely not answer PMs