For the first 5, next 15, and every subsequent 20 Chum Eggs (up to 100), the Chum Queen will give you a Chum Queen Tear. Each of these will increase your Stamina gauge substantially.
No more tears will be given after you’ve collected 100 eggs; instead you will be awarded the Chum Mask, which can detect any nearby uncollected eggs. If you collect a further 40(?) eggs, you will be given the Chum Top. To complete the outfit, collect the remaining 25 eggs and you will be awarded the Chum Skirt.
High quality version.
Most of them are located near Fast-Travel waypoints, and you should be able to find 100 of them by normally progressing through the game. Due to the scale of the in-game world, it is not feasible to display the map at a greater zoom level.
Tip: To check which eggs you’re missing and the region they are in, go into your save file (C:\Users\USERNAME\AppData\LocalLow\Shedworks\Sable\SaveData\sable_data_XXXXXXXX) and look under “ChumsMonitor”.