Instant File Initialization
Easiest way is to 


enable TF 3004 and 3605 (turn them off when done)
Create a dummy database
Check in error log for "SQL Server is zeroing out ..."


SQL Server 2016 will log the message by default when Instant file Initialization is enabled ... instant file initialization is enabled

Obviously, you can use xp_cmdshell whoami /priv or tsql way.

Good PFE blog reading : How and Why to Enable Instant File Initialization