Which LIB should I link with

getenv is not a Windows API, it is a 'C' api (so does not require the call-convention winapi)

GetEnvironmentVariable is a Windows API

You can use COBOL syntax to get an environment var..

   accept my-home from environment "HOME"

Thank you.

than as follows call without winapi and link with libc.lib, include stdlib.h and 

libpath=c:\\Program Files (x86)\\Microsoft Visual Studio\\<version>\\VC\\lib
Set INCLUDE = "C:\\Program Files (x86)\\Microsoft Visual Studio\\<version>\\VC\\include"
set LIBRARY = "C:\\Program Files (x86)\\Microsoft Visual Studio\\<version>\\VC\\lib"

version = 2019

Net Express works with the C runtime from Microsoft Visual C++ 6.0

Later Visual COBOL products, do support VS 2019 and you can find details in this document:

www.microfocus.com/.../Application_Compatibility_Guide.pdf