There are 2 problems I see with your code - 1st missing CommandName property in aspx code and you can follow solution proposed by @Jignesh Khant.
2nd you are missing event handler in your aspx code for datalist control. For that you should specify event binding for Itemcommand i.e.
onitemcommand="outerDataList_ItemCommand"
the way you have done it for
onitemdatabound
event.
Without event handling Asp.net Runtime would never know that outerDataList_ItemCommand function is handled by
outerDataList's itemCommand event.