how install electrum-ltc?
The instructions for linux on the front page (https://electrum-ltc.org/) are for debian which whonix is based on, so they will work. Just run those commands in the workstation. I should note that it requires installing packages from pip which is usually discouraged because it doesn’t use package signatures.
TemplateVMs don’t have network access for anything except the package manager, so pip won’t work there unless you assign it a netvm.
Because of the above and because using pip is unsafe, I suggest you create a standaloneVM based on whonix-ws and install it there. And only use that new standaloneVM for electrum, not browsing.
if I use the instructions for the Bitcoin electrum from the documentation whonix to pass through the tor, is that enough? or something else you want?
Enough to do what?
You should prefer APT when installing packages. Third party package managers should be avoided.