Umbra's supreme gems post https://plarium.com/forum/en/throne-kingdom-at-war/599_fan-guides/45142_assailants-jewels-tab/?post=421026 will be your long term friend.

There really aren't any jewels or runes for Assailants or Apostates.

The only useful jewel is Citrine for March Speed https://throne.help/en/resources/gems/411/

- x 6 slots.

- only 6 slots, as the Inquisitor isn't used when attacking Ass.

There is also Malachite for +250 x 6 Total Stamina https://throne.help/en/resources/gems/412/ and Nephrite for +3% x 6 Hero's Stamina Restoration https://throne.help/en/resources/gems/413/

- but as it takes 54k stamina to kill an Alpha (the only Ass. worth killing, aside from n6's), the gain is so little, and the increase so miniscule, that the jewel slots may as well be used for other things. (Particularly when growing and one only has one profile or set of equipment.)

However, don't forget the Leaders Boosts:

(If you have Hero's Stamina restoration, use it, otherwise, ignore it.)

And, often overlooked, the Dedicated reputation:

You may also find searching for 'attack' at https://support-portal.plarium.com/en/throne-web/faq/ useful.