Can any doctor examine that girl has had a sex before? by any method or technique?

Only one test: There is one "test." You just ask the person (but be sure you have a reason to ask). A girl can ask a guy how many people he has had sex with. Likewise, a guy can ask a girl how many people she has had sex with. This test has better accuracy when guys are being asked, because there is more negative stigma for a girl to have had several sex partners. To be fair, stigma should apply equally to guys.

No: There is no 100% reliable "virginity test".Girls can be born without the hymen that some use as a proof or it may be lost in childhood by non-sexual contact. There are also many forms of sexual contact than can spread STD's but not involve vaginal sex. In short if she has a kid or an STD she is not a virgin, beyond that her word is the determining factor.