Jenos can 1v1 weaker enemies very well, he can pump out some decent damage and then use his Void Grip to allow his teammates to gank you. If you are able to, try to continually shoulder peak him so that he can't Void Grip you, or take a teammate.
Be ready for Jenos' ult. You have plenty of time to move out of the way as long as you are ready for the tell. Also, consider buying Resilience to shorten down the void grip if either they have it's legendary, or if you have no mobility.
Someone recently mentioned that when Ruckus uses his ult he can't move so use Jenos' ult then. Even if you do that it won't kill him since he's a high health tank unless he already has half of his health down. Instead see if your enemies are cornered
Jenos is very flexible and can fill in many roles (except frontline) with any loadout. Try to find his play style and adapt accordingly.flanking? Group up. Damage? Flank him in a group. Healer? Cauterise.