Nikyo can be done so in many ways.  Here are a few that I have seen:

• Two hands on the uke‘s wrist and that wrist is pressed tightly against the shoulder of nage as in kihon.
• Two hands again, but the uke‘s wrist is out a ways from nage (needs strength but adds distance)
• Uke’s wrist pressed against nage’s shoulder with one hand on the wrist and one hand on the elbow (beware sankyo kaeshiwaza)
• Like above, but the second hand comes under the elbow with nage’s palm facing him like looking at a mirror (good for backhand atemi)
• Two hands on uke‘s wrist while te-no-ko is pressed against nage’s forehead (can henka into sankyo)

All seem effective if the nikyo motion curves towards uke‘s hara.