Can Welding Jar target itself?
Welding Jar can target itself.

When you cast a spell or activate an ability, you choose targets (601.2c) before paying costs (601.2g). So the Welding Jar is still on the battlefield when it's time to choose targets, and is a valid target for its own ability.

That ability will fizzle, of course, since you've already put Welding Jar in the graveyard by the time it would resolve.