What is the interpretation of verse 94 of Surat Yunus?

The exegetes differed regarding the addressee of the verse (Yunus: 94). Some said it was addressed to the Prophet, peace be upon him, and its meaning is: if you are in doubt about what has been revealed to you, then ask the impartial People of the Book. Others said it was addressed to the polytheists, and its meaning is: Say to these polytheists, if you doubt the Qur'an, then ask those deeply rooted in knowledge from among the People of the Book, such as Abdullah ibn Salam, because they acknowledged the People of the Book's knowledge. Al-Qurtubi mentioned other interpretations, among them that the address is to the Prophet, peace be upon him, but others are intended, or "Say, O Muhammad, to the disbeliever." He clarified that "doubt" (shakk) in the language means narrowness. And that the particle "fa" (then) with conditional particles does not necessitate an action, citing the Prophet's saying, peace be upon him, when the verse was revealed: "By Allah, I do not doubt."