How do I collect DIAMONDS, NOT GEMS, in game??? I cannot manufacture them from what I can see so how do I collect them???
You get diamonds from playing daily Dungeons (unlocked after beating Drifting Sands quest) and you can get some from your guild when you finish weekly tasks with gold
Complete daily dungeons, complete weekly guild tasks, and also by completing weekly events such as invasions, raids,etc…
In addition to the methods listed above by others, diamonds are craftable in the soulforge as shown in the following picture:
Be aware that the soulforge needs to be at least level 9 to craft diamonds from shards.
Here is a more general article that reference finding diamonds