What does it mean to 'queer a text'?

Honestly, I think you mean "query" a text...as in ask questions of its basic assumptions.

Actually no it doesn't mean "query" it means "queer!" To queer a text is to subject it to questions regarding identity formation, to "deconstruct" it, after Derrida, to reveal its inherent bias in regards to questions of normative subject identity particularly as it pertains to questions of sexuality. So perhaps yes it involves "querying" but only insofar as the "asking questions of its basic assumptions" are directed towards an undermining of the assumption that heterosexuality is "normal" or "real" or assumed in discourse be a fait accompli.

Ah! So academic nonsense that only English postgrads care about. Thanks!