"scientia hominum" could mean both anthropology (the study of human beings) and "human knowledge" (the corpus of all knowledge acquired by human kind).
How do you distinguish between the two (i.e. how to translate those two concepts in a non-ambiguous way)? A more general question would be how to distinguish between a possessive and a subject of study.
Latin has both a possessive and an objective genitive, and so scientia hominum can well mean both "knowledge possessed humans" and "knowledge about humans". Using the genitive will always include this ambiguity.
You can use the adjective humanus, "related to humans". But the relation implied by such an adjective is flexible, and scientia humana can well be understood in both of the two senses.
If you want to have separate words for these two concepts in a text, you can make pretty much any choice you want but you need to explain it. I do not think that Latin has a good concise way to express these two things without ambiguity so that both terms point unambiguously to only one of the concepts. My preference is to use anthropologia and scientia humana but to explain the intended meaning of the latter. The explanation need not be explicit; your use of the terms in suitable contexts will ease the reader into how you use these words.
With that all said, the most compact unambiguous phrasings I can think of are scientia de hominibus for anthropology and scientia quam homines habent for human knowledge.
This is closely related to the question about philosophia naturae/naturalis.
As Joonas said, this comes down to a distinction between subjective and objective genitive. When a noun is derived from a verb, a subjective genitive indicates the logical subject of that verb ("human knowledge" = humans knowing something), and an objective genitive indicates its logical object ("human knowledge" = something knowing humans). See A&G §348 and thereabouts for more discussion of this.
In Latin, the most common way to express both of these is with a plain genitive (scientia hominum). However, there were a few particular ways to get around this ambiguity.
In particular, objective genitives could often be replaced with prepositional phrases, while subjective genitives generally could not. (For example, Cicero generally uses odium alicuius to mean "someone's hatred", and odium in aliquem to mean "hatred of someone".) Conversely, subjective genitives could be linked to nouns by esse, while objective genitives generally could not.
Extending this to scientia, see Cicero's Pro Sulla, where he links a subjective genitive with esse and replaces an objective genitive with a prepositional phrase:
Nam cuius scientiam de omnibus constat fuisse, eius ignoratio de aliquo purgatio debet videri.
For when a particular person is assumed to have knowledge of everyone [involved], his ignorance about someone ought to be seen as proof of innocence.
Literally, here, it's knowledge concerning everyone (prepositional phrase with de), and this knowledge is assumed to be belonging to someone (genitive linked with esse), making it unambiguous which is the subject and which is the object of scio.
