They are quite easy to spot - you will see the red dot in a window (what the wand interacts with) and no marking on the floor so you know that is a hidden one.
DD also asked some of the cms working there - (they stand in costume near the spells) to check she had found them all.
Spoilers - don't read if you want to discover them yourself
My husband found a list online while we were there. I found it challenging to spot the red dots during the day. But like the previous poster said, it was very easy just to ask the witches or wizards in the area.
Also there are 'surprises' if look for them. For example, in knock turn alley one of the spells unlocks a door. Be sure to turn the knob