Learn Croatian: Otkad radiš kao pčelar? - Since when do you work as a beekeeper?

In Croatian, if an action started in the past and is still ongoing right now, you use the present tense. Because the word otkad (since when) implies the action is continuing into the present, the present tense radiš is the correct choice here.

Are otkad and otkada exactly the same thing?

Yes. Otkad is just the shortened version of otkada. Both are formed by combining the preposition od (from/since) and the question word kad or kada (when). You can use either form interchangeably.

Why is pčelar (beekeeper) in the nominative case here? Doesn't the preposition kao require a specific case?

Unlike most prepositions, kao (as/like) does not force the following noun into a specific case. Instead, the noun matches the case of whatever it describes. Since it describes 'you' (the hidden subject of the sentence, which is nominative), pčelar is also in the nominative case.

I recognize pčela (bee) inside pčelar. Is -ar a standard suffix for professions?