They're OK (clear) but not perfect. The 'at' is questionable. At first I thought it should be 'on', but then I read 2. Shouldn't they both be 'on the wooden shelf on the front desk'? The two 'on's are not ideal; you could replace the second one with 'above'.
By my ear, 'at' wouldn't be right - but it's OK when the 'desk' isn't so concrete: Before leaving in the morning, please hand your Comments slip in at the front desk.
Some people get upset about 'fill in'/'fill out'. I don't - I'm not even sure which I tend to use more.
Student or Learner