We do know, and the answer is absolutely not.
The human mind does not store data and information like a computer, in discrete memory units or 'bits', but in the way the neurons in the mind interconnect, and in how the synapses form between these neurons. The mind is NOT a sequential digital device, but an analogue wholistic device.
The information is not in the actual synapse, but in the pattern of these synapses throughout the mind.
In order for information to be 'downloaded', all existing synapses would have to be destroyed, all existing neurons would have to be destroyed and regrown, every current reconnection of neurons and synapses destroyed, and a very time-dependent process of sending each and every new downloaded piece of information, in absolutely the correct sequence, with the exact emotional state and tagging assigned to it, through the new neurons to form entirely new synapses and interconnections.
Essentially, you are growing and building a completely new mind.
And even at that, there is absolutely no guarantee that the new mind will process exactly the same information in exactly the same way.
Information in the human brain is completely integrated with the emotional system. It is moderated by the emotional state of the mind at the time the information was gained and processed. The interconnecting synapses are made larger or smaller, inhibited or complimented, by the emotional state at the time they are formed. There is no conceivable way a 'download' could recreate the emotional state at the time every single piece of information was stored. That information would also have to be incorporated into the download - a complete history of the complete timeline of the emotional state of the person over their entire life, co-synched with the presentation of the data itself.
Any concept of 'downloading' or 'uploading' the human mind exists in fiction and fantasy only. Any instance of this concept in fiction completely ignores how the human mind both operates and functions. Inevitably, the author ignores reality and substitutes their own version of it, their own artificial and completely ludicrous concept of the human mind, in order to accomplish their plot device.
If you want to use it as a plot device, go ahead. However do not ever expect that
anyone can give you a scientifically, neurobiologically valid method for accomplishing it.
I also failed to mention that human 'memory' is actually distributed throughput the body. Our responses, reflexes, and such are located in muscles and synapse junctions throughout the spinal column and further down the system. We remember how to spell, in part, through muscle memory. How many times have you, in response to 'How do you spell...', trace the word out in the air with your fingers? That is muscle memory for the correct spelling of the word. The act of talking relies on reflex memory in the tongue and such. Emotional memory is in fact and reality part of the response of the gut. Emotional memory is VERY visceral.
So not only do you have to 'download' the 'brain', you also have to download the entire body to preserve ALL of the memory, skills, responses, intricacies, and personality of the human 'mind'.
But please, all those proselytizers that still say it is possible, please explain EXACTLY what is the difference in the human brain between that moment when it is alive, and that moment when it is STILL exactly the same lump of protoplasm, cells, neurons, interconnections and such, EXACTLY the same, only dead? There is NO physical difference in composition between a live brain and when, a few seconds later, it is dead.
That dead brain is an identical, complete copy of the former live brain complete in every physical molecular detail. An atom-by-atom recreation. In fact, exactly the SAME atoms, in exactly the SAME structure. If the exact same physical thing is no longer functional as a living brain, how can one be even mildly serious about producing a 'downloaded recreated copy' of that brain and still have it work as a living brain?