Hello,
This is polish officers infantary gorget from XVIII centuary.Why Wettin symbols on top of eagle?This time polish king was from Saksonia/Wettins family:August II and after his son August III.
Please find below link to official website of Polish Army Museum with similar gorget:
http://www.muzeumwp.pl/emwpaedia/ryngraf-oficera-piechoty-koronnej-z-pierwszej-polowy-xviii-wieku.php
Brgds