First and foremost, let me just state, I think I get where you're coming from. You have legitimate concerns: What do they have in common? What experiences and mutual understanding could they even build a healthy connection on? Could they possibly have a meaningful future together in the long-term? Is he just using her or taking advantage?
I'm going to suggest something that the other answers touch upon, but in a more actionable, what-can-you-do-right-now way: Re-word these concerns into questions, and ask your daughter these questions. Try to word them so they don't give off an impression of being against the relationship: I think you'll get the best results by opening the conversation with the attitude that you're just curious and want to genuinely get to know what your daughter is currently going through better.
That's not to say that you shouldn't already disapprove - while I personally wouldn't start feeling disapproval just from what you've described, your feelings are very understandable - but regardless of how you might initially feel, you can always tell her you disapprove a little later, once you've gotten as much of her perspective as she's willing to share. But at first, it's better if you can be simply inquisitive: You don't want her to feel like you've already made up your mind before you've had a chance to thoroughly discuss it, right? I think sometimes people just disengage and become resistant to anything we say if they feel we're already against what they're doing, which reduces our ability to actually help them significantly.
Approaching with an inquisitive attitude helps everyone involved: If you ultimately decide you disapprove or that there are real concerns, you'll be able to present your position much more thoroughly, pointing to the concerning details from what she herself has told you. In the process of asking her these questions, she might even start thinking about issues she might have overlooked herself. And maybe in the process, you'll learn something about why they're drawn to each other and how they both think and feel that makes you feel more comfortable with the whole thing.
Personally, I'd just start with something like "hey, I was just wondering, could you tell me more about how this relationship started and what made you like him?". Unfortunately, it can be hard to find a way to word things without causing misinterpretations. For example, at least where I'm from, a curt and direct "So what do you see in him" can give a very negative, even judgmental impression, even though taken literally it's almost the same question. So maybe soften it with clarification, like "don't take this the wrong way, I'm just asking so that I understand what you're thinking and feeling, because I've decided that since this relationship seems to be important to you, I want to fully understand where that's coming from".
I think this a good starting point - it immediately gets at the root of investigating how much your concerns apply to this specific case, helps lead your daughter to spotting any problems that might be looming in this relationship without just making her feel like she's being told "no", builds mutual understanding and a possibility of openly discussing relationships, including the tough parts, between you and your daughter, and has the opportunity to show her by example what kind of questions to ask when figuring out if a person is right for her in a relationship.
Best case scenario, she and her romantic interest will positively surprise you with mature and well-considered perspectives on why they're right for each other. But if not, I think the above will put both you and your daughter in a better position to navigate any troubles that might come up, together.