"Koblížek" literally means "little kobliha". I don't know if this means a literal size difference or if it's just a casual diminutive (ie. the common -ek/-ka endings). Hoping for a native Czech to enlighten us. :) To be honest, donuts aren't something I encountered much in CZ. A quick check of Wikipedia tells us that kobliha is closer to a jam donut/Berliner, whereas the regular hole-in-the-middle donut is just a donut.

it is kobliha :)

KOBLIHA is the right answer. In THE SIMPSONS is it also translated as KOBLIHA. But kobliha is only similar to donut, not really the same, but the word kobliha is used also for donut and also for that czech kind of donuts. You can use also the word DONUTKY (plural) (read dońootkee) - it is not often used, but it is more correct for real donuts (but never used with that czech version of donuts).