I had some great notes on this but I think I wiped them.
You need to make sure you're linking everything together, cause and effect.
Dispossession means, as bored of sc said, the removal of the Aboriginal peoples from their land, "their country".
This is the same country to which The Dreaming has forged for them an inextricable connection.
EVERYTHING revolved around Country. It defined who they were, where they could go.
The loss of contact with this land resulted in the loss of access to Sacred sites, totems, wtc. especially when you compare the traditional practices of the Aboriginal people compared with the upbringing which they were subjected to in missions etc.
For the "Stolen Generations" disposession has also meant loss of kinship ties with their tribe, also inability to have their rites of initiation. Thus spirituality is affected.
Furthermore, this loss of kinship and contact with elders has resulted in the loss of hundreds of languages from all the tribes which were in existence before disposession. As the Aboriginal culture relies strongly on verbal tradition and communication, this has furthermore led to loss of oral tradition, and spiritual practices.
P.S. This is probably not everything you need to discuss in a full assessment task but I hope this has helped in some way.. this is all off the top of my head so if I think of anything else I'll post it.