Using Cemeteries/Search Cemeteries, find the cemetery page in the Find a Grave app. Once you are on the cemetery page, tap on the list of memorials or to find only the photo requests, tap on the button that includes "# Photo Requests."
Choose from the Search, Filter, or Sort options menu lower on the search results page. Under Filter/Advanced options you'll see many options, such as Grave photo, No grave photo, GPS, No GPS.
The icons to the left of the memorial specifically reference what that memorial needs, the map pin for GPS and a headstone icon for the photo. Swipe left on the memorial in the list to easily add either of those to the memorial.