"Dompetmu diambil siapa?"

Translation: Your wallet is taken by whom?

[tsuj1g1r1]

Is "oleh" optional or do you have to memorise which verbs take it and which don't?

[Rick392366]

Is "oleh" optional or do you have to memorise which verbs take it and which don't?

'oleh' is optional in this sentence.
'oleh' = 'by'

'oleh' is used in combination with di- verbs (passive).

[1CN5ijzC]

if we use "oleh" to identify the doer / person who do the verb, we can omit it

[poompah]

Who took your wallet?
This is almost always going to be the used form of this sentence. The literal translation accepted is correct of course, but will almost never be heard or used in normal conversation.

[KamoSaru]

But if they put the English "Who took your wallet?", the learners would always translate it into "Siapa mengambil dompetmu?" and never have a chance to practice translating it into "Dompetmu diambil oleh siapa?". Literal translation is sometimes good for beginners.

[JarrodMain]

'was' should also be accepted.

[TakeYoshim2]

The English example sentences must be considered to renew so as to be more appropriate English and current English.