Since no one else has said so, there are a few families of words that are regularly derived from more general suffixes. -aĵo to mean "meat of __ animal" is such an example. Of course -aĵo has many other meanings, but this is a convenient way to derive the meat from the animal.

-ujo (container) as "bush/plant containing this fruit/flower" is another such suffix: rozujo (rosebush), pomujo (apple tree).

Since no one else has said so, there are a few families of words that are regularly derived from more general suffixes. -aĵo to mean "meat of __ animal" is such an example. Of course -aĵo has many other meanings, but this is a convenient way to derive the meat from the animal.

Actually that was my original point. I have been told that -aĵo means "meat of __ animal", but the examples given at lernu.net for araneaĵo, and azenaĵo do not follow that rule.

And so far, nobody has answered my question of how to say donkey-meat. Is "azenviando" the right word?

Yes, "azenviando" is right word, but

eoru.ru:azen||o осёл, иша́к (тж. перен. — об очень глупом человеке);
~a прям., перен. осли́ный;
~aj oreloj осли́ные у́ши;
~a obstinego осли́ное упря́мство;
~aĵ/o
1. осли́ное мя́со, осля́тина;

2. глу́пый посту́пок или выска́зывание;

vortaro.net:azenaĵo
1 Viando de azeno.
2 Stulta diro aŭ faro.

So "azenaĵo" also is good for "donkey meat" and is its 1st meaning.