Why are the adjectives always placed after the pronoun "something"? For example: "Something black", "Something else", "Something funny" ... Also are there any other pronouns like this one?
All the compounds with some/any/every/no+thing/one/body work this way. These are historically noun phrases, with thing/one/body acting as the nominal and some/any/every/no acting as the quantifier-determiner. If the compound is treated as two words, an adjectival would naturally be placed between the determiner and the nominal:
some black thing
any honest body ... note, by the way, that body in this generic sense of "person" survives today almost exclusively in dialect
But when you re-analyze some+thing as a single word you lock the adjective out of that position, so it has to be placed after the nominal:
Traditional grammar analyses "something" as a pronoun, but a more modern approach takes it as a compound determinative.
There is a constraint on the position of certain modifiers called 'restrictors' that can be used to modify such compounds. The restrictors (adjectives or certain nominals) cannot occur in pre-head position because of the fused nature of the construction and are forced into post-head position, with only "else" allowed between them and the head:
“nothing (else) significant”