1- How can i re-install the CAL again in the new windows while i forget/lost the licence key of this CAL.
can you remember when or where you bought windows server 2012 rds cal ,in general ,we would receive email about windows server 2012 rds cal package key from reseller.
if we bought windows server 2012 rds ca from volume license center ,can you logon volume license center then check if there is RDS cal product key or agreement number information about w2012 rds cal.
in general ,if we don't have license key pack id or agreement number information about w2012 rds cal,we can not enroll w2012 rds cal on RDlicensing server 2016.
microsoft volume licensing services center
https://www.microsoft.com/Licensing/servicecenter/Help/Contact.aspx
2- if i installed windows server 2016 , is the CAL 2012 working in the windows server 2016 or not?
yes.we can enroll w2012 rds cal on w2016 RDLS server ,but we need to have license key pack id or agreement number information about w2012 rds cal.if we can not find these information ,we need to buy new rds cal again indeed.
Install, Configure and Activate RD Licensing
https://www.youtube.com/watch?v=r_fMZ9qFAA8