In most cases, @vancoder's answer is absolutely correct. My situation appears to be fairly unique, but I want to share my experience so it may help someone else.

In the case of this Nevada theme, the standard functions are not used in the template files. Apparently, Nevada uses the Lambda framework (something totally foreign to me) and so any text output occurs with a lambda_translate function call. After digging and digging, I gave up on trying to trace these functions back to a `__()` or `_e()` call.

Instead, to find the text domain, I put on my Linux hat and entered this command in the Nevada theme folder.

    grep -r "load_theme_textdomain" .

Sure enough, in the functions.php file, the load_theme_textdomain function was there with the text-domain.