Generally speaking you may not know something is illegal but most laws can at least be broken down to something you specifically did without any subjectivity what so ever. Did you kill the guy? Did you transport that bird? Did you lie on your resume? Did you beat your spouse? After the charges are explained in a court of law you should be able to know with certainty whether or not you're guilty and be able to plan your defense and plea accordingly, but it's likely that you won't know if you failed prongs two and three of the miller test.
- Whether the work depicts or describes, in a patently offensive way, sexual conduct or excretory functions
- Whether the work, taken as a whole, lacks serious literary, artistic, political, or scientific value
Did you make something patently offensive and does it lack serious literary, artistic, political or scientific value? That's a question for which you may not be able to reasonably answer.