Where is the second word of power for Kyne's peace?

Solution 1:

The 3 walls with the words to Kyne's Peace are in Ragnvald, Shroud Hearth Barrow and Rannveig's Fast

I'm not sure which quest you did, as it may have been a radiance quest, so you'll have to see which on these places you've been to before. I linked entries to the Elder Scrolls Wiki to provide you with more information.