When it comes after nouns, it is a usage of the following meaning:
[副助]《代名詞「なに」に副助詞「か」の付いた「なにか」の音変化から》名詞、名詞に準じる語、活用語の連用形、一部の助詞などに付く。
1 一例を挙げて示す。…など。「この着物―お似合いです」「映画―よく行く」
2 ある事物を例示し、それを軽んじていう意を表す。…など。「彼の言うこと―聞くな」「君に―わからない」
For the definition #1, it translates mostly as or something. For #2, it is a way to degrade the noun.
On the other hand, a prefixed なんか works as something similar to a indefinite article or some.
So
- アルバイトなんかある人 : people who need to go to a part-time job or something (it could be something other than job).
- なんかジャケット : some jacket (the speaker is not specific about which jacket, but it will be jacket and could not be a coat).
Note かなんか, which is literally or something, may be more widely usable for the post-fix なんか, but they are not totally interchangeable with なんか. For example, この着物かなんかお似合いです is odd. In this case, by 着物なんか, the speaker suggests this kimono (among other things), for example.