Annotate block in Proteus
You need to select your block, then click with right button like in the picture shown bellow



Proteus automatically will copy the block and it will show the copied block in some sort of degraded view like the image shown bellow (attached to the mouse cursor)



then finally you can make a left click on any place of the sheet where you want to place the new block, isis will annotate it automatically for you like in the image shown bellow where connectors J1 and J1-1 were copied and named J11 and J12 respectively (on the left side of the sheet).



I hope I could help you