How to get engineers and scientists? | FAQ XCOM 2: War of the Chosen Game Guide

The right amount of Engineers and Scientist is one of the most outstanding elements needed for victory in XCOM 2; it's pretty much the same in the War of the Chosen. The engineers are used for excavating rooms, building stuff and manning facilities - they are able to improve the efficiency of different centers and unlock additional capabilities of these. The scientists, on the other hand, cut down the time needed to finish research projects, especially when you build a Lab - if you do that; the scientists also provide a much better chance of Breakthrough and Inspire. They're also useful in the Shadow Chamber.

You can recruit new personnel by completing Covert Actions.

The same places are used to acquire scientists and engineers:

• The Black Market - each time you get resources from the Council, new items will appear on the Black Market. Among them, there may be engineers and scientists ("purchasable" for Intel points).
• Finishing missions - probably the best way of obtaining personnel, available as rewards for some missions - oftentimes awarded for Guerilla Ops missions. Sometimes they are the VIPs that need protection. Always check the prize for each mission and opt for those that offer additional personnel - there are other ways of obtaining soldiers, resources and items, and they don't require that much effort.
• Finishing Covert Action for the Resistance. Some of them will also yield an engineer or a scientist.