From my understanding there's only two ways to access the event schedule-
The event calendar was implemented on Dec 3 2018 according to an official news article on Tibia.com:
A brand-new event calendar, which can be found in the redesigned login screen of your client and in the news section of our website, informs you on currently active and upcoming events in Tibia.
Sadly from my understanding you can't go see the event schedule on the client when your logged in the game. A workaround would be of course to go on Tibia's website or logout back to the login screen.
Congrats shawtay on 10,000 reputation points!!!September 15, 2020
Outstanding Contribution contestSeptember 14, 2020
Hints for posts that received a down-voteAugust 15, 2020
I've received a down-vote - how can I fix it?August 14, 2020