My father in law wants me to be his partner in a store that sells cigarettes and other tobacco products, or at least to give him money to help him open such a store even if I don't become a partner. What's the view of Islam about owning a tobacco store or helping someone open one?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Smoking is forbidden since it harms the human body and its harms have been proven through medical research.
Allah Says (interpretation of meaning): {… and prohibits them as unlawful Al-Khabâ'ith (i.e. all evil and unlawful as regards things, deeds, beliefs, persons, foods, etc.), …} [7: 157].
Allah also made forbidden everything that harms us. Allah Says (interpretation of meaning): {… And do not kill yourselves (nor kill one another). Surely, Allâh is Most Merciful to you.} [4: 29].
When Allah forbids a thing He also forbids selling, purchasing and promoting that thing. Ibn Hibban narrated in his Sahih that the Prophet (Sallallahu Alaihi wa Sallam) said: "When Allah forbids something He also forbids its price" .
Therefore, it is not permissible for you to make investment with your father in-law or to lend him money for this project since it is cooperation in sin.
Allah Says (interpretation of meaning): {… do not help one another in sin and transgression. …} [5: 2].
Moreover, you should advise him and show him this Fatwa.
Allah knows best.