ἐρωτητέον
From LSJ
ἐν ταῖς ἀνάγκαις χρημάτων κρείττων φίλος → it is better in times of need to have friends rather than money, a friend in need is a friend indeed (Menander, Sententiae monostichoi 143)
English (LSJ)
verb. Adj. A one must ask, ἐρώτημα Arist.APo.77b7.
Greek (Liddell-Scott)
ἐρωτητέον: ῥημ. ἐπίθ. τοῦ ἐρωτῶ, δεῖ ἐρωτᾶν, Ἀριστ. Ἀναλυτ. Ὕστ. 1. 12, 2.