Reddit mentions of Welding Metallurgy

metals and how to weld them is a good book. It's more practical prescriptive knowledge "if you have aluminum do this, if you have brass do that".

Sindo Kou's book welding metallurgy is awesome!
"http://www.amazon.com/Welding-Metallurgy-Sindo-Kou/dp/0471434914" Its my go to book for refreshing my brain on welding metallurgy, although that's more technical on the metallurgy of melting stuff if you want to know the engineering side

hobart has a very good book series that is one for each weld process can't seem to recall the titles, I still keep them around when I teach welders. I'll warn you welding is not a trade that can be taught from a book, kinda like painting or sculpture the technique is too complex to really describe.

As a metallurgist, I must suggest Welding Metallurgy if you really want to get into it.

These have served me well.

http://www.amazon.com/Welding-Print-Reading-John-Walker/dp/1590706420/ref=sr_1_1?ie=UTF8&qid=1405115134&sr=8-1&keywords=blueprint+reading+john+walker

http://www.amazon.com/Modern-Welding-Andrew-D-Althouse/dp/1566379873/ref=sr_1_2?ie=UTF8&qid=1405114998&sr=8-2&keywords=modern+welding

http://www.amazon.com/Welding-Metallurgy-Sindo-Kou/dp/0471434914/ref=sr_1_1?s=books&ie=UTF8&qid=1405115261&sr=1-1&keywords=welding+metallurgy

Your coworker was suggesting Welding Metallurgy by Sindo Kou, however I have no idea what type of material would be on the CWE exam.

Good luck to you!