You should at least now the basics of Mendix. But this path you probably are the most interested in: https://gettingstarted.mendixcloud.com/link/module/98/lecture/824/Introduction
My assumption is that at least you want to retrieve all the data from IOT devices and then REST is the way to go.
can i retrieve data from other iot cloud and monitor the assets in this cloud ?
This is such a broad area that there isn’t a one fits all solution. I’d start with some questions:
These links to community webinars might help you: