By giving a presentation in a meetup. They now are all online but if you have a good idear you can contact Jan de Vries from Mendix on the slack channel.
Recently I completed that challenge, you can choose any latest topics prepare yourself and start recording your presentation with screen sharing, audio and video if you wish. Then finally send the recording to Mendix support for credit points. This is also one of the way you can complete the presentation challenge.
Hi Dirk Fraanje,
The quest to do a presentation about Mendix and the credits that come with it, can be obtained via proof (a meetinginvite, a list of attendees, an online webinar with the URL, a videopresentation and the link to the video ...) via firstname.lastname@example.org. The more info you can provide, the faster you’ll obtain the credits.
I hope this helps you further.