Nimbostratus
Cirrocumulus/mgmt/tm/asm/policies/ will show policies from all partitions.
However, make sure you are not also logged with the same account via GUI.
The GUI session will set the partition for your user that impact your REST requests, so if you logged with Common, you will only see policies from Common, if you change to another partition, you will see for Common and the other partition.
You can filter the output for a specific partition as well:
/mgmt/tm/asm/policies/?$filter=partition eq partition2
However, that is a filter for what you were already getting from the /mgmt/tm/asm/policies/ .
If you are logged vi GUI in the Common partition, you will not see policies in partition2 even with the filter.
I just tested this in my lab with version 14.1.2.2.
It did took me a while to understand the GUI was having impact :D.