I have graphics layer on client side with buffers around location with different radius: red -10km, yellow-30km. Is it possible to have legend which will be printed on the map using esri print widget? Or is there any other option to achieve it?
Unfortunately, the print widget will not include symbology for GraphicsLayer instances. However, you can achieve this by using a client-side FeatureLayer instead. See more info in this sample, and under the documentation here (click "Read more" under the section "Creating a FeatureLayer" and scroll down to the "Add an array of client-side features" subsection).