Elementless help....

I’m confused. I got an elementless jewel 2 finally. About to do my last optional quest against Kushala, unless more pop up lol. I was going to use The last Odo LBG Karma. It has no element, but the jewel doesn’t boost my attack. BUT the jewel only fits my helm slot. So does it have to be equipped to the weapon? And also...does elementless work on all weapons that have no element? Like the weapons that have elemental damage in (parenthesis) and it’s grayed out? Thanks in advance for the help. I mean, it says “equipped weapon” so that makes me think it doesn’t have to be slotted on the weapon 🤓