"Who is here?"
I'd say, "Хто там?" is super common, like when somebody is knocking at your door, and "Хто тут?" is when you are coming back to your bed after riding the fridge at midnight and the room is dark and scary and suddenly you feel some movement... But then it becomes "Хто тут??!!"
I've been typing in the Latin transliterations up until now, but it didn't accept "Xto tut". It's a bit inconvenient for me to put in the Cyrillic text, since I would have to use a converter or memorize the Ukrainian keyboard layout. So...what did I transliterate wrong here?
In English transliteration, the Ukrainian "ХТО" ("who") would be spelled as "Khto". The Ukrainian "x" sound is pronounced as "kh", as in "хата" ("khata").
To simplify things, I would suggest you go to the Google 'Play Store', type in 'Ukrainian Keyboard', choose & install a high-starred Ukrainian keyboard app. Then you can type in Ukrainian.
It's not as difficult as you think. (Just make sure you choose 'Ukrainian' not 'Russian' as both are different languages and have different letters.)