Is it possible to get hiv by going down on a random woman with toungue?

No risk: Same as the reply to your question about kissing. HIV has not been known to be transmitted by cunnilingus (oral-vaginal sex). No significant risk. To avoid sexual acquisition of HIV, avoid unprotected vaginal or anal sex, and don't worry about any other sexual practices.

Exposure is unlikely: Many things are "possible" in life, even if rare, but do the math. There are about 320 million people in the U.S., so 160 million are female. About 80% of them are older teens and adults, which is 128,000,000 people. About 25% of the 1.2 million HIV-infected people here are women, which is 300,000 people. The chance of your RANDOM woman just having HIV is 300,000 / 128,000,000 = 0.0023 = 1 in 500.

Zero risk: HIV isn't transmitted this way. Lesbians who do this simply don't catch it. You can get gonorrhea, syphilis, and a few other less famous illnesses. Casual sex always carries some risks of interpersonal troubles. I'm glad you're safety-minded and hope that love brings you happiness.