I know "Join Curves" command has been replaced by newer functionality "Composite Curve" and is no longer readily available in 1899.
However, as far as looking at the release note, it seems that the command is still available by environment variables. Please give me the environment variables to be available for this command.
Solution
The environment variable was only available till NX 1899 and the command has been completely removed in NX1926.
The solution is:
Join Curve – now use the Composite Curve->Join Curves = Yes option.