local function OnGossipHello(pUnit, event, player)
    pUnit:GossipCreateMenu(100, player,  0)
    pUnit:GossipMenuAddItem(0, "return number 1", 1, 0)
    pUnit:GossipMenuAddItem(0, "Return number 2", 2, 0)
    pUnit:GossipSendMenu(player)
end

local function OnGossipSelect(pUnit, event, player, id, intid, code)
    if(intid == 1) then
        print(1)
    end
    if(intid == 2) then
        print(2)
    end
    -- basically could just do print(intid)
end

ALTERNATIVE:

local function OnGossipHello(pUnit, event, player)
    pUnit:GossipCreateMenu(100, player,  0)
    pUnit:GossipMenuAddItem(0, "return number 1", 1, 0)
    pUnit:GossipMenuAddItem(0, "Return number 2", 1, 0)
    pUnit:GossipSendMenu(player)
end

local function OnGossipSelect(pUnit, event, player, id, intid, code)
    if(intid == 1) then
        print(id)
    end
end