HK1 = Holding Confirmed with the digit indeed meaning the number of seats in this res.

If your res should say RQ1 that means that they are requesting a seat for you and you are on some sort of waiting list, but not entitled to a seat assignment.

by the way, the class of service...Y or F or V T K etc. is printed right after the flight number. So for example your res could say:

CO 126Y 28May SEA-IAH HK1
CO 126F 28May SEA-IAH RQ1

meaning you are confirmed in a coach seat but waitlisted (RQ) in First Class.

Clear?