For people who are confused about what a kagune is. I'll explain. I'll also explain what a kakugan is as well.
A kagune is a ghoul's predatory organ that functions as a weapon or claw. It is usually red (but it varies), it's flexible like water, but firm and sturdy.
If you want to know more about a ghoul's kagune, then go to Tokyo Ghoul Wiki. :)
Now for the kakugan.
A kakugan denotes a ghoul's eye where the iris turns red, and the sclera turns black with red veins across the eye and into the skin around the eye.
The ghoul can enter this state by their own will, but this state is also entered when a ghoul is excited, extremely hungry, or when they use their kagune.
Ghouls generally have two kakugane, and they always activate together. But there can be one-eyed-ghouls with only one Kakugan.
If you want to know more, go to Tokyo Ghoul Wiki.
I hope this was helpful. Have a nice day/night.