perhaps i wasnt clear before when i mentioned that hoid could have held adonalsium.
i thought that since he was there when it shattered it was possible he was holding it at the time and the shattering could have forced him to take on his physical form again. an event similar to when ati and vin died there bodies reformed and dropped to the ground. accept since adonalsium shattered and not his mind like in vin and ati's case he would still be alive.
this would explain his knowledge of all the shards and their natures because he would have once held them and retained his knowledge of them. it could also explain how he can "planet hop" using the cognitive realm, and everything he apparently knows about all the shard worlds like in mistborn, he always seems to be around important events. he might know when and where these events would take place because he was there before as adonalsium and would have had some ability to see the future.