According to Trekwood's website, it looks like a 14"x22" skylight. That said, it could be any measurement since Keystone routinely substitutes components on one assembly line if they run out of the intended parts, so your "Summerland could have a Cougar skylight, a Passport skylight, a Fuzion skylight or any other part that was in stock when the line shut down with your trailer waiting for parts....
https://www.trekwood.com/parts-searc...23+%2F+Keyword
So, to be sure, ALWAYS CONFIRM MEASUREMENTS... but it probably is 14x22... And, if the "skylight is broken", you'll need both the outer dome and the inner dome. It's a "dual dome system" one on the outside and one on the inside...