There is an online course on cartography being run by esri which will probably be quite good. Information about registration can be found here. It runs from April 18 to May 29, 2018.
I recently completed a MOOC run by esri on Spatial Analysis and it was excellent. I can highly recommend it and they are running the course again in April. It runs for 6 weeks and provides a nice introduction to ArcGIS online.
When I first became interested in data viz I did a MOOC run by Alberto Cairo and it was really enjoyable. In 2017 the Knight Center for Journalism in the Americas is running a MOOC called Data Exploration and Storytelling: Finding Stories in Data with Exploratory Analysis and Visualization. Check it out here, it should be good. So far the first 1000 people who have registered come from 81 different countries. The course starts on 16 January 2017.