Hi. If you are still around this is what is different abut sky Q.
'On Demand' is no longer a menu option in its own right but is incorporated into various other options. For example, say you have forgotten to watch call the midwife and want it on demand. You can : go to the 'catch up' menu where you will be able to view it through iplayer, or do a search for 'call the midwife' where yu will have a choice, where possible, to download (on demand) or record the episode you want that is playing at a different time.
In short 'on demand' has been replaced in the main menu by either 'catch up' or by doing a 'search' for the programme you require.
Sky Q has a few issues including a very clumpy menu but once you get around that its better than the previous sky box.
HTH