You simply can't.
Even if you were to do some off-enjin server stuff, there is no API method for accessing events / calendar items.
The best you could do in your current situation is to make an announcement in a forum thread or news post and rss that through the rss->slack (enjin integrate)->discord webhook hack.
1) Get rss link of forum or news
2) Integrate your site with Slack
3) In Slack, get the RSS app to use on your workspace
4) Create an outgoing webhook that is linked to your discord channel webhook (with /slack on the end)
But, with all that said, it would just be easier to make the post on Discord.