Yes, an offline layer is basically an AGSFeatureTableLayer. This layer has a renderer. You can get to the symbols being used by the renderer and ask for a swatch of each symbol. These swatches can then be displayed in a legend.See https://developers.arcgis.com/ios/api-reference/interface_a_g_s_symbol.html#a64ad2116214fae6b0b0609a...Also see Offline Feature Editing Sample. This sample gets swatches for all the symbols being used by the offline layers and displays it in a Feature Template Picker. This is similar to the code you would need to display in a legend.
