Thank you. What is the indicator for this Dative sentence since I cannot ask "Wem". These are the sentences that are most frustrating for me since a person is not the indirect object:
Ich habe an meinem Geburtstag gearbeitet.
"Ich" is the subject, "gearbeitet" is the direct object and "Geburstag" is the indirect object. So I should remember that "when" sentences are also Dative. Is that correct?