I'm not aware of any built in functionality to display graticules but you can possibly accomplish this using some layers available in AGOL. This link will take you to an AGOL item that has 1,5,10,20 degree interval lat/longs. These lines were created by ESRI for the Firefly basemap option so you'll probably want to re-symbolize them to better fit with your app.
On the AGOL item page, just copy the Service URL link for whichever lat/long lines you want to use in your app and add them as a layer into your app as you would normally do.
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