I'm new to the 17th shard community so please do excuse me for any mistakes on my part and feel free to give your opinions on this. I don't know if this topic has already been covered, anyway I'll get to it:-
I was bored so i thought i'd re-read the dueling scene of adolin, Kaladin and renarin against the four shardbladers. While doing so I came across a particular section.
After renarin dismissed his blade, he closed his eyes and looked upward, "exposing his throat". When reading for the first time I initially thought he was giving up and accepting his faith, and that the reason for relis to hesitate was because he didn't want to strike down the defenseless renarin.
On re-reading though, I thought it had something to do with his surgebinging ability as a "truthwatcher". I figured he used his surge - and to do so closed his eyes and looked upward - this showed relis a memory of his past and made him hesitate. In another chapter renarin had told his father that it wasn't a sin to look into the past when conversing about dalinars visions so I believe being a truthwatcher has something to do with the past (given that renarin was the one who told that)
Earlier it was noted that syl saw something close to renarin, I still don't know if she was referring to pattern or glyss.(or both)
This is my opinion and it's a complete speculation but please do give your feedback as well as your own theories of the abilities of "truthwatcher"