This is a Plastic Bubble skylight. This type of skylight was popular in the 70’s and 80’s. This type of skylight sits directly onto the roof deck and has no flashing, which are angled pieces of sheet metal that step in with each row of shingles used to protect against leaking.
This type of skylight WILL leak. It is no longer a standard manufactured item due to the problems in the past. There are enough problems with this type of skylight that we cannot warranty this area unless the skylight is replaced with a skylight that has the proper flashing installed, as shown here.