To me, a "witness story" is a book that tells about someone's faith journey, or part of their faith journey. I have read several in this category and I will continue to read them to help push me further in my own faith walk.

"The Hiding Place" by Corrie ten Boom

"God's Smuggler" by Brother Andrew

"Case for a Creator" by Lee Strobel 

"Seeking Allah, Finding Jesus" by Nabeel Qureshi