If you want to know who attacks your Allies without asking them each time, you can set up incoming Reports about their Cities. You can receive Reports on all Raids, Political attacks, Spy activity, and Sieges of their Cities.
Such an option is available for all players in the game. However, it can be activated only if both sides configure the Reports for the Allies. It can be done in the "Diplomacy" Reports settings.
When you open the settings, you will find two tabs: "My Reports" and "Allies' Reports". In the "Allies' Reports" tab, you can select friends who will receive the Reports about your City. Your Allies need to do the same if you want to receive their Reports. Please note that you will not be getting the Allies' Reports until they select you in their "Diplomacy" Reports settings.
After the Allies have been selected, please go to "My Reports" tab and mark the types of the Reports you would like to receive. Do not forget to Save the changes when the selection is done.