A colleague of mine who's also my subordinate has sent me inappropriate emojis (kissing and the likes) few times. How do I put him in his place?

Yes tell him that it is a work platform and his communication should be professional at all times

Put it in his butt

It’s a tricky one but as he doesn’t seem to be getting the message maybe just tell him gently that his emojis are making you uncomfortable and you’d appreciate him saving that kind of stuff for his wife.

Sometimes the professional, direct and polite approach is the best in these situations. If it was me I would send him an email or text saying “please don’t send me the emojis, they make me feel uncomfortable, thank you” In these situations it’s also very important to create a paper trail including all evidence, you’d be surprised how these things can come back and bite you even if your not at fault.

That is totally inappropriate and he should know better . Put him in his place .

Tell him it's not appreciated, and that you'll involve HR should it continue ! Save the messages as evidence.

Take time to state his professional boundaries for you.
Then demote his job description to only making you coffee.

Just ask him how are his wife and child. Talk about them every time he does that.

Tell him bhosdk he will never do that again

Just never send any back. You don't need to talk about it, he'll get the hint after a while.