iPhoto to Photo migration

Photos for Mac does not support event. Instead of "events" there are now the "Days". in Photos 5 and Photos 6, or "Moments" in Photos 1 to 4. See: Moments in Photos are the New Events

Your old iPhoto events should have been migrated to Photos as albums. These albums should appear in the sidebar under "My Albums" in a folder "iPhoto Events"

What do you mean by "iPhoto Library"? Do you mean the library Photos created from your iPhoto Library?

If you mean to merge your Photos library with the migrated-from-iPhoto Photo's Library, the easiest way is to get the (paid) PowerPhotos from Fat Cat Software.