Currently, my wife is buying back her pension for the time that she was on maternity leave. Where do I enter her buyback amount for 2018?

[TurboTaxKim]

Report this in the RRSP section. When you go to your RRSP Profile, check the box next to 

"Claim for undeducted contributions made to a Registered Pension Plan (RPP) or have contributions for past services"

and continue to the "Registered Pension Plan Deduction" page to make your entries.