Suggested Farm #1: exit the Serenity Temple and make a brief loop through Pockmark Flats (as shown). Any L20 character should be able to solo this using any build.
Threats & Recommended Skills
Tactics: foes that drop Scorched Lodestones are L8 or less, so L20 characters only have to worry about how to dispatch the elementals more quickly. Aggro a group, wait for them to ball up, and use AoE damage spells to take them down.
Threats: presuming that you have at least one L20 character with access to Ascalon, none of the foes will present much of a threat. If you want, bring a well-balanced skillbar that includes hex and condition removal, healing, with the remaining 5 skills dedicated to damage.
Recommended Skills: (see above)
This is a great week to try out solo farming for the first time or practice using a new build. As mentioned above, any L20 character should be able to safely farm without paying too much attention.