The most direct way is to ask her. Before you do, understand fully why you need to know. If all else fails, ask her wife.
tell him the reasons why you are a lesbian...he will understand.
You can tell if you are a lesbian if you are attracted exclusively to other women.
If you are a curious and need to tell if you are a lesbian, think about a woman's body. If it turns you on in a sexual way, you are likely a lesbian.
You ask her.
You ask her.
That your a lesbian
Try to educate them on what bisexuality actually is. Tell them "I am not a lesbian. Lesbians will only date girls. I'm bisexual. That means that I don't care about gender. I care about the person inside."
They can't tell from an exam. The only what they can tell is by asking you.
Ask her
That your a lesbian
No, you can't tell unless they tell you, or you find them in a sexual situation.
The only way to tell is to ask them. There are no physical signs.