Those all seem to be frames from Load On Demand addons so you're probably trying to hook them before they exist.
What you need to do is find the Blizzard addon they belong to.
Create a frame and register it to recieve the ADDDON_LOADED event.
Check which addon loaded and if it's one of yours, hook the script eg.
Lua Code:
local f = CreateFrame("Frame")
f:RegisterEvent("ADDON_LOADED")
f:SetScript("OnEvent", function(self, event, addonname)
if addonname == "Blizzard_GarrisonUI" then
GarrisonLandingPage:HookScript("OnShow", function(self)
-- do whatever
end)
elseif addonname == "One of the other addons" then
-- do whatever else
end
end)