What version of Maximo are you on? That is the 7.6.0.X UI, but some chose to revert to that even on 7.6.1.X versions. In 7.6.1.2 (
IBM Software RFE Community: View request) my RFE for enabling sorting through relationships was supposedly added. We tried testing this but never got it to work even in demo apps on the most basic 1:1 relationships such as INVENTORY->ITEM. It's possible it depends on enabling some setting that we're not aware of but we tried to analyze any new settings that were created and didn't find any that seemed relevant. We haven't opened a case with IBM yet, but if you're on 7.6.1.2 I would definitely do that.