I wrote to the MN DNR to get the details on the MN watercraft trailering decal.
Here is what I received from the DNR - use the link below.
http://trailers.mndnr.gov/
The link above should get you all the answers you are looking for. The law I believe you are referring to is for a trailer decal, not a permit or license. It will be required if trailering any water related equipment in or through Minnesota. It is a 30 minute online training presentation.
Walt E.