So, following your advice about quotes at least, it looks like this...
$result=mysql_query('SELECT * FROM wkho_TTX.users WHERE email="$email" AND mobile="$mobile"');
No dice. I'm interested in why the variables need to be in single and double quotes? I've never seen that before
No, that will not work. You have placed your double quotes inside the single quotes and your variables are still part of the string. So the variables will not be converted. If you really want to write it out like that you should invert the quotes.
$result=mysql_query("SELECT * FROM wkho_TTX.users WHERE email='$email' AND mobile='$mobile'");
You require the quotes around your variables because you are comparing string values, numbers do not need them. And you are placing the whole lot in a pair of quotes because PHP needs to pass the query to the database engine as a string.
I just prefer not to use the string parsing feature of PHP.