The prohibition on homosexual sex in the Hebrew Old Testament is restricted to male-male contact only. Because having multiple wives is permitted in the Torah (as evidenced by the statement that you shall not take a mother and daughter both as wives, or competing sisters - something to keep in mind in this polyamorous world we know as NY ), the Hebrew laws would have had something to say about permitted touching among women because simultaneous sex would be assumed to be at least a theoretical possibility.

The fact that no statement is made about this means that, essentially, (1) lesbian sex and (2) female masturbation are permitted. It may be that they're permitted because no one really thought about women when writing the laws - they were by men, for men and with men in mind.

It could also be that, since the main interests of the society were propagation of offspring and knowing the paternity of any children, those two acts were considered irrelevant as long as the man was doing his procreational duty. I think it's less likely that the latter was the reason, though, because there is no injunction against heterosexual oral or anal sex in the Old Testament, and it can be argued whether or not the "sin of Onan" was the actual act of male masturbation or the failure of Onan to perform the required Levirate marriage sexual acts.

I tend to think that it was because the Torah is a male-oriented work of literature. After all, the definition of "adultery" is when a man has sex with another man's wife or a woman has sex with someone who isn't her husband. This sly definition thus allows married men to have sex with prostitutes (as long as they're not temple prostitutes, which would make the sex act a consecrated offering to a foreign god! ), unmarried women, random girls they pick up on the road to Bethany, women they decide to rape while performing sacred genocide or otherwise capture as spoils of war, and the near obligatory sex with slaves, maidservants and other personal property of a human nature.

As a result, from an Old Testament perspective a woman could know herself or another woman with legal and moral impunity (of course, "legal" and "moral" in the Old Testament are essentially the same concept).

Of course, the Christians had to ruin this situation. Polygamy is discouraged, marriage is expressed to be the "preferred state" if one is going to have sex, ordinary prostitution is decried and we have the famous statement in Paul's Letter to the Romans that directly decries not only male homosexuality, but female homosexuality as well. It is worth noting that the statement in question says "even their women did change the natural use into that which is against nature, and likewise also the men, leaving the natural use of the woman, burned in their lust toward one another" (King James Version). It's not the best translation of the Greek, but even in the original the verb used for the women is to "exchange" one for another, and for the men it is to "forsake" the one for the other. As a result, I think that there isn't a clear statement on female bisexuality even at that point. An argument could be made, therefore, that as long as a woman isn't strictly lesbian that she is permitted, even in the New Testament, to know another woman.

As for knowing oneself, there is no direct injunction against it anywhere, and of course "Know Thyself" (Gnothi Seauton) was the motto written above the Delphic Oracle, so everyone in antiquity would have been familiar with the statement.