Does no one else use "Target of target"?

[Viridiana]

tanks shouldn't be required to mark. There's a little thing called /assist to help you hit the target they are. marking certainly helps but as a dps, you shouldn't need your hand held.

Works pretty well. . .unless the tank is hopping around targets too much. Not common, but I have (rarely) encountered aggro issues because I was assisting at the wrong times and hitting lesser targets. Pretty much the only reason I like marking. If #1 is alive and #2 is nomming my face, it's my fault. If #1 is nomming my face it's almost certainly the tank.

That said, in the absence of marks I just aim at whatever got Shield Lobbed.

[LunarEmerald]

I always assist with the first target the tank hits (almost always the shield lob) few tanks shield lob one target and attack something else. I stay on that target unless the aggro color changes to orange then I look for another or wait a few seconds.

[BondEternal]

I use "Target of Target" for Eye for an Eye on my SMN and BLM so that I don't need to change targets to apply Eye for an Eye on the tank.

As for knowing which mob to attack when the tank doesn't mark, I just look at what the tank is attacking and attack the same one.