May I say: "The workout is in the gym" ?
I think you can since the verb "to be" is not required.
You would need an article in that sentence - i believe it would be цей (but maybe a native speaker could clarify).
No, you do not need the word цей here. By the same token, цей is the noun determiner "this," not an article. Ukrainian doesn't have articles.
Since it's not a complete sentence and isn't punctuated, "a workout in the gym" is a perfectly correct translation. It's not mandatory to use the verb "is" in this exercise (no pun intended). They marked me wrong.
Could we not say simply "gym workout"?