Hello! You have lots of questions which is a good thing. The Centers for Disease Control and Prevention has a great website with facts about STDs, how they are spread, and how to protect yourself. I think it would be a great idea for you to look over the site: https://www.cdc.gov/std/healthcomm/stdfact-stdriskandoralsex.htm
Who is at more risk of getting STD. The one giving oral sex or the one getting the oral sex?
If a girl has some STD, will she transmit STD if she is giving blowjob to boy or boy will get it if the boy is licking her vagina?
If I use condom for oral sex (Girl sucking me), Condom you say will help me get any STD right?
What about if I want to taste and lick girl's vagina? Dental dams are not easily available. Any other way to protect myself from STD and have fun?
Unless there is direct contact of mouth with genital, there is no way to get STD right?
Assuming she has some STD (all of this is true of anyone you have a sexual encounter with, not just CSWs) -
1) Kissing on mouth - no risk for an STD, but she might have oral herpes which you might get if you don't already have it. This would be herpes type 1.
2) Kissing breasts - no risk for anything
2) Cunnilingus - slight risk for gonorrhea
3) The girl kissing my penis - just lightly kissing - no risk; giving you actual oral sex - if she has oral gonorrhea or oral herpes, you could get these genitally (if herpes is transmitted this way, you would get genital herpes type 1). If you already have herpes type 1 (cold sores, fever blisters), then unless she has an outbreak, you can't get it genitally.
4) Body to body massage using nuru gel - no risk for an STD
Unless someone has physical symptoms you can see (sores, discharge), you can't tell if someone has an STD. Using condoms is a great way to protect yourself, and since you don't plan on having actual intercourse, your chances are much lower. Plan on her using a condom for oral, and you should be fine. If she has signs of any symptoms, then gently decline to have sexual contact with her.
Good for you for getting info first. :)