You can use the Foreign Slip to report the foreign employment income.
Then use the "other deductions" to report the exempted portion:
you can access this from the search engine on the top bar or from the left side menu --> deductions --> other deductions --> miscellaneous --> continue to the next page "Additional deductions"
Use the "other" box and add a description such as "exempted foreign employment income under a tax treaty"
You should be able to see the amount on line 25600
I hope this was helpful