Or it´s even possible?
Yes, it's possible.
It is not showing on every wallet start because it is not really secure, but it's still possible since this key is a part of wallet keys.
If you really want to get it with wllet loading, then in this file "src\wallet\wallet2.cpp", find that line:
LOG_PRINT_L0("Loaded wallet keys file, with public address: " << m_account.get_public_address_str());
LOG_PRINT_L0("Loaded wallet keys file, with public address: " << m_account.get_public_address_str()
<< ENDL << "tracking key: " << m_account.get_keys().m_view_secret_key);
With that modification you gonna have tracking key showed on each wallet load, but as i said - it is not really secure to have tracking key in logs.