[Choonstertwo]

In addition to what Seerah said, you don't check which event fired by calling their names (e.g. GOSSIP_SHOW()), they're not functions.

kgPanels provides the OnEvent handler with an event argument whose value is the name of the event that fired.

So the code would look like this:

if event == "GOSSIP_SHOW" or event == "BANKFRAME_OPENED" then
    ChatFrame1:Hide()
    ChatFrame3:Hide()
    ChatFrame1ButtonFrame:Hide()
    ChatFrame3ButtonFrame:Hide()
    ChatFrameMenuButton:Hide()
    GeneralDockManager:Hide()
    FriendsMicroButton:Hide()
else
    ChatFrame1:Show()
    ChatFrame3:Show()
    ChatFrame1ButtonFrame:Show()
    ChatFrame3ButtonFrame:Show()
    ChatFrameMenuButton:Show()
    GeneralDockManager:Show()
    FriendsMicroButton:Show()
end

Keep in mind that you need to register these events in the OnLoad script if you want them to fire for your panel.