Ruling on working as a manager in a restaurant that sells haram things

May Allah reward the questioner with good for his eagerness to seek halal provision. If he continues to do so he will succeed in sha Allah in this world and in the Hereafter. Allah says (interpretation of the meaning):  

“And whosoever fears Allah and keeps his duty to Him, He will make a way for him to get out (from every difficulty).

3. And He will provide him from (sources) he never could imagine. And whosoever puts his trust in Allah, then He will suffice him. Verily, Allah will accomplish his purpose. Indeed Allah has set a measure for all things” [al-Talaaq 65:2-3]

As for working in this job, it is haram so long as the restaurant sells haram things, even if the one who holds this job does not do the selling himself, because he is helping with something haram. Allah says (interpretation of the meaning): 

“Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allah. Verily, Allah is Severe in punishment”

[al-Maa’idah 5:2]

Imam al-Jassaas said in Ahkaam al-Qur’aan (2/429): The apparent meanings of the words of Allah “Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety)” indicates that it is obligatory to cooperate in everything that is obedience to Allah, because birr (righteousness) is obedience to Allah. And the words “but do not help one another in sin and transgression” mean that it is forbidden for us to help others in disobeying Allah. End quote. 

And Allah knows best.