Since most questions have been answered I will do my best to explain the rest....
Chicken scratch...it is a treat of mixed grains. It is a treat to be used sparingly. A small handful flung wide will get them "scratching" around doing chicken things.
BOSS is black oil sunflower seeds. It is also a treat and can be flung wide along with the scratch. Treats are any edible item other than their formulated feed. Treats should only be fed at about 1 Tablespoon per bird per day so the protein in the feed is not diluted with low protein treats.
How to tell if a chick is in an egg... This can only happen if the rooster is breeding the hens AND the eggs are being incubated. Incubation is done with a hen who has the hormones triggered to sit on the nest and be "broody". No you cannot make a hen go broody. The second option is using an incubator.....that is a process I have not done so cannot advise there.
To know if a chick is growing in the egg a strong flashlight and dark room are often used. This is candling and the light lets you see what is or is not going on in the egg.