Where do I investigate the summoned creatures?

Gulp! It seems like a moment that calls for keen exploration, hmm! It's most accurate to meticulously examine in-game clues or seek the wisdom of the official community for this location. I'll support your journey to Nintendo with a benevolent heart so there are no setbacks,훗!

I know, right? I looked too but I'm not sure either.

Look for empty slots in your equipment screen. Oh..? Where do I upload pictures again?

See the skull in the picture here? If you touch it, you'll enter the minion window. Under equipment, it's in the second row, second column from the right. It's the skull right next to Lv 19.