Translation:Was he trying to eat the soup with a knife?
Disclaimer: I could be completely wrong, but...
MAYBE there's a perfective/imperfective mismatch with "sníst." "Snažit se" is imperfective, as is "jíst," while "sníst" is perfective. But since this is just a GUESS, you might try reporting it if you get the exercise again.
I fear we may just be missing the gerund variant. I have added it.
what is the difference here between: did he try to eat, and was he trying?
Disclaimer: I'm not a grammarian, so this is not authoritative -- and this course is teaching Czech, not English. But... for most everyday usage, there's probably not a significant difference between "did he try" and "was he trying." However, the first suggests that he tried and stopped trying fairly quickly, while the second suggests that his "trying" continued for a longer period. Compare these two sentences: (a) Did he try eating the soup with a knife and quickly switch to a spoon? and (b) Was he trying to eat the soup with a spoon for 10 minutes before he realized it wouldn't work?