28-year-old Himachal Pradesh batsman, Dogra was in fine form in the Ranji Trophy last season, scoring a double hundred, a hundred and a couple of half-centuries.
He also scored a half-century in the domestic Twenty20 against Jammu and Kashmir last month.
Dogra represented Rajasthan Royals in 2010 before he was roped in by Kings XI Punjab last season.
A veteran of 10 domestic seasons, 31-year-old Narwal of Delhi was prolific with both bat and ball in the 2010-11 season scoring 340 runs in eight matches and picking up 40 wickets at an average of 20.22.
"He can take the new and old ball and can contribute valuable runs in the late middle order," a Knight Riders statement said.
The likes of Yusuf Pathan, Manoj Tiwary, Debabrata Das and Rajat Bhatia have been a huge letdown as Knight Riders have a difficult task to make the last four after suffering five defeats from seven matches to slump to seventh place.