how to know a girl that is she virgin or not

You can not tell by vaginal inspection.

So how can you know?

1. Get to know the girl mentally and spiritually. You will learn about her life-style, her interests, her spiritual life, her morals, her hopes and fears, her strengths and weaknesses ... and so on. You will learn to trust her (or not). Then when you ask her, you will know whether to believe her.
2. Now think about how a girl can know that you are a virgin. Apply similar criteria.

If you find a girl who is a virgin, what will you do? Sadly, there are many men look for a virgin girl, rob them of their virginity, then move on. I trust you have more virtue than that!

If you are looking for a girl you can marry as a virgin bride, that is admirable, but she has the right to expect the same from her groom.

If, having got to know the girl mentally and spiritually (as above suggested), and you grow to love her, and then find out that, despite her moral strengths and great character she is not a virgin (maybe she was raped), what will you do? Will you have the moral courage to respect her for what she is now, and marry her?

You do not indicate in your question the reasons behind it, so maybe I have not answered the question sufficiently. Is it a moral question? Is it a cultural issue? Is there a religious aspect?

Hope this helps.

I look forward to your response.