“Find a place to secure a transmat zone for the Tower.”
“Find the Breach” is an objective in the mission The Dreadnaught in Destiny: The Taken King
Turn to the left. You can see a massive hole in the side of the Dreadnaught. This is where you want to go. Head over to the left and then make your way over to the opening.
When you approach, you will see a small white circle. This is your target. Enter the circle and you will have the prompt to plant a beacon. Ghost will summon your ship and it looks like you can exit. This does tend to draw the fight of any nearby forces. Be ready for that. Wait for the conversation between Zavala and Cayde to finish. You have one more thing to do.