Below are the locations of the ampersand in each level. Note that collecting one in itself is not sufficient - even though it will appear on the book pages, if you quit and reload without actually finishing a level, it will not save that it has not been collected - you need to collect it in a set of attempts that actually concludes with you finishing a level.
Gothic (§2)
After q collectable, gain speed on the q platform then jump to the next letter and instantly again to get to the loop above the main path. If you don't have enough speed, travel to the left to die and respawn on the q platform.
Garamond (§3)
To the left of the q collectable, fall down between the o and p platforms, and then swim down and left.
Didot (§1)
Swim down to the g collectable in the water, keep going down and enter the little passageway on the right.
Clarendon (§3)
After entering the saloon, travel up the v and w platforms and onto the flat platform, then move left and jump up to the next layer of platforms, and right again to ascend to the highest level of platforms where this ampersand is.
Futura (§3)
Stand on the riser where you collect the u collectable. Then rather than heading right towards the v collectable, you are going to head left. Be careful not to get crushed by the red circle - if you don't think that you can make it, wait as the elevator will lower and then come back up. Jump to the light blue triangle on your left, and then across the grey and yellow platforms to reach this level's ampersand. Note that these triangles (especially the first) will move when landed on - if you fall or die and then they are in the wrong position, they will not reset until you reload the whole checkpoint.
Times (§1)
After collecting the e collectable, you enter a pipe that moves to the right, and at a t-junction heads down to continue the level. If you jump back into this pipe after exiting it, it will instead take you up to the top of the level, where you can collect this level's ampersand.
Helvetica (§3)
Upon entering the hippy section, you will see an ampersand as soon as you start falling. If you miss it on the way in, ride up the left wall and then jump across to it, as you have unlimited jumps to make this collection easier than it appears (despite the reversed directions, visual effects, and slow movement making it feel more clumsy generally).
Pixel (§3)
Immediately upon entering this section, before the jump towards the n collectable, you will see a glow coming from the bottom of the screen. Drop down there to collect the ampersand.
Comic Sans (§-)
Shortly after the rainbow, the bouncing P can be used to launch you up and to the right, to where the ampersand sits to the left of the R suspended in midair. Note that you will have to move quickly through this section to stay ahead of the cat and have time to collect this final ampersand.
N.B. You may not need this one as this is a secret level and the achievement says eight, but I got it before some of the others so can't check.