SG1008D desn't support to receive power from a POE source.
And I didn't hear about the feature of POE pass-through.
If you want to use an external PoE injector, it doesn't need switch to support any feature, switch can only provide the data connection and POE injector combine the data and electricity. Switch doesn't need to support POE.
So if you just only want the terminal equipment receive power from POE, just connect as ----Switch----injector----terminal equipment.