Yes they are the same exam - it was originally created for VCP6-NV but is still valid today for the current VCP-NV 2020, and is on the NSX-V product.
VCP-NV 2020 is the certification you will be awarded when you complete the various requirements, don't worry about VCP6-NV as new certification holders cannot be awarded it.
There are currently 2 tracks for VCP-NV 2020 - for NSX-V and for NSX-T: VMware Certified Professional - Network Virtualization 2020 (VCP-NV 2020)
Given the direction of the NSX product, I would expect future exams to be on NSX-T only - you can take the NSX-T path today, so the NSX-V exam retirement should be less of an issue.
To answer your other questions:
Exam Number - 2V0-642 - is this exam retiring on June 30, 2020?
Yes
if yes, then whether this date will be extended in view of the ongoing Covid-19 Pandemic ?
For most countries, remote testing is now available - so I doubt it.
Pearson onVue is not available in Japan, thats why i cannot take exam online from home ?
Correct.
Can i use some VPN to connect to other country and attempt the exam ? will it work ? will it be legal ?
That would be a question for VMware or for Pearson VUE.
I would strongly advise sending an email to certification@vmware.com
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