There are six manifestos scattered across Havarl for you to read- each is on a datapad marked ‘Roekaar Datapad.’ Note that these datapads do not disappear or deactivate once read, so you may accidentally 'discover' the same manifesto more than once. The six manifestos are:
Legacy: Find this one inside Thaldyr's quarters during Jaal's Friend or Foe questline.
Conquerors: Inside a cave in the north of the Chasm of the Builders, by a fallen Roekkar, guarded by a Galorn.
Fire: On the upper platform of the Roekaar camp on the far side of the bridge over Chasm of the Builders. This bridge becomes available during the main Havarl questline.
Invasion: on some shelves in the building in the south side of Old Pelaav.
Hope: on a desk in a building on the north side of Old Pelaav
Truth: This is in the Roekaar research camp north of the Old Courtyard. You can onyl reach it during or after the Overgrowth quest, which in turn requires that you've solve the Havarl Vault.