"Although [whale sharks] produce eggs, they don't lay them. Instead, the young hatch while still in the female's body and are born as miniature adults. This is known as ovoviviparity." [1] The More You Know.
So, technically, the largest egg, as in laid egg, is the ostrich's (around 6 inches), although, the largest egg in relation to body size belongs to the kiwi (25%) [2]. For more eggs facts press 1.
[1] https://www.nhm.ac.uk/discover/do-sharks-lay-eggs.html
[2] https://savethekiwi.nz/about-kiwi/kiwi-facts/enormous-egg
