Brake shields if that's what you are talking about, are sandwiched between the unit bearing and the knuckle. Looks like you are missing them entirely or they rusted away from their base which is sandwiched between the bearing and knuckle. To add or replace those you would just undo the 3 unit bearing bolts, pull the bearing and axle shaft together and put the new brake plate on, then reinstall the bearing and shaft, sandwiching the plate to the knuckle.