Well... to be honest... I don't know what "giving him head" is. (What can I say, I'm old.) I presume it refers to something sexual. You mentioned your daughter is 18. So I presume where you live she's an adult. She would be where I live. And under those circumstances, to my way of thinking, she's free to do as she pleases. It's really not your business. (Personally I don't think the fact that she's a cheerleader in high school really has anything to do with it.)

The one caveat is that presumably she's still living at home with you & your wife. So you certainly do have some say with regard to what goes on in your home. Consequently, at least from my perspective, I would say the only thing for you yourself to do or say is... nothing... unless you & your daughter have a particularly close bond to where the two of you are comfortable discussing intimate subjects. To my mind, all you can likely do by intervening after-the-fact is make the situation significantly worse than it is.

I think what perhaps might be appropriate would be for your wife (since she's the one who caught your daughter & her bf in the act) to tell your daughter you & your wife would prefer she refrain from performing sexual acts in your home. (My thinking would be that if you & your wife try to have this discussion with your daughter together it's likely to come off as much more of a confrontation.) And of course make sure she's on some form of birth control, if she's willing to be, & if she's going to be sexually active. I'm assuming your daughter, & probably your wife or maybe even you as well, have discussed the ins-&-outs of human sexuality over the years as your daughter has matured.

The reality here is your daughter is now (presumably) an adult & she & her bf may have been doing this (& perhaps much more) for some time now. And although you may not want her to be performing sexual acts in your home, the reality is there are worse places she & her bf could go to do it. So ultimately, at least from my personal, non-professional perspective, I think the "watch-word" here is to tread carefully. It would be very easy to turn this unfortunate incident into something all three of you will come to regret. My best wishes to you.