Student or Learner
which one is grammatically correct?
"The toecap at/in/on the front of the shoe is curved"
I would use "on" if I were forced to use your sentence construction but I would like to point out that the whole thing is rather tautologous. The toecap is always at the front of the shoe, that's why it's called a toecap - it covers your toes. I would use "The shoe's toecap is curved".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.