How can I get the yield of my purified immunoglobulins?
You can use western blotting with a anti IgY secondary antibody conjungated to  a HRP (or other reporter), this method will primarily help with troubleshooting your purification and locating IgY in the different fractions and flowthroughs.

If you want to quantify, consider using an ELISA kit. Here is one such kit (https://www.antibodies-online.com/kit/1563240/IgY+ELISA+Kit/)