If there was any premine of DASH how much was it?
There was never any premine of Dash. Premine means mining before public launch, this was never the case with Dash.
Dash had some bugs in its software, when it first forked from Litecoin code base which caused a production of a large number of blocks
with the maximum allowable coins in each block during the first two days of Dash existance. This was then fixed by the lead developer
and the blocks got created as intended. Those that profited were basicly the miners that were mining Dash in those first two days.
Most of those miners sold Dash at large quantities on the open market.
What happened to Dash is called an instamine, and it can in general include a number of issues. Ranging from faulty code (Dash)
to one entity holding million of coins (Satoshi / Bitcoin) to abusing mining software by hamstringing it with regards to speed while
favouring a select few miners on secretly faster running mining software (Monero).
To lean more about Dash instamine and how much it exactly was :
https://dashpay.atlassian.net/wiki/spaces/OC/pages/19759164/Dash+Instamine+Issue+Clarification