Just as you see an extra icon at the lower left when you send a march, a similar but different icon appears when marches are incoming. (You can see examples as you send attacks to and from an assailant.)

Click on the icon and you can see details.

Or, press 'k' for 'Marches to go to the 3rd tab of the council hall. Or 'w' for the Watchtower.

Off the top of my head, I forget which shows which, but if you go to the 1st (Info) tab of the Watchtower (Outpost), at the lower right you see a red 'More' button. Click it to view how much gets shown when.