Chronos. There is rarely a reason to get anything else for Jenos except Chronos if you're intending to heal with him. If you find yourself being hard-countered get Chronos II then buy another item to properly defend yourself.
Nullify, nullify, nullify. Bait Maeve into the open, then hit her with the good ol' Nullify beam. More often than not, her Nine Lives will still be on cooldown, and someone else is gonna be there to kill her.
If you have the Focusing Lens legendary, Skye can be countered if you use a Front Line as your meat shield. That Skye has nowhere to teleport; landing all five shots on her will be more devastating than you think.
The educated Strix player knows not to attack you when you're in Counter. The key to getting him is to fight fire with fire and be as stealthy and sneaky as possible; and be ready to react when he inevitably pulls out his sidearm.
In the event the Evie is using Reprieve and relying on her Ice Block, Scorn would be a great counter. Be wary, however; the relatively skilled Evie players can just blink away and have you gone seconds later