The local rivals will meet in the first leg at Headingley on Sunday, May 1 (3pm), and in the second leg at Castle Park on Sunday, May 8 (2.30pm).
The two-legged play-off final will be played on Wednesday, May 18, and Wednesday, May 25 (both 7.45pm).
Meanwhile, Knights this week announced the signing of full back Sean Scanlon from Rotherham Titans for next season.
The 27-year-old can also play on the wing.
Director of rugby Clive Griffiths said: “He’s a very good counterattacking player and will add strength and versatility to the squad.”