Is it 'chwe' or 'chwech' dolffin? Both were in this lesson I think.
As explained in the section notes, this is a known error, it should be chwe, and chwe is an acceptable answer in the course database where it is required. (It is not a terrible error to make in conversation, though, as your meaning would be understood well enough!)
There is no need to report incorrect chwechs - they have already been identified for correction.
Yes, the Duolingo app has no notes. However, if you have a connection to the web you will be able to use your device's browser to access the web-site version with the notes.