connect Mac Mini to Imac running El Capitan

For what purpose?

If your intention is to use the iMac as a monitor for the mini, forget it. The combination is supported in neither hardware nor software. Target display mode is dead technology.

The new Mac mini cannot use an old iMac as a monitor.

+1 What are you attempting to achieve by connecting the two devices together?? As mentioned if you want to use the iMac as a display for the MM, it's not going to work period.