You can use as
$name = $your_array["name"];
$email = $your_array["email"];
$address = $your_array["address"];
$gender = $your_array["gender"];
$city = $your_array["city"];
$hobbies = '';
foreach($your_array["hobbies"] as $key=>$val){
$hobbies .= $val.' ';
}
And finally you can use the above variables in the email code.
Update from your last comment, you can do the way you are doing as
foreach($data as $key=>$value) {
$body .=$key."=";
if($key== 'hobbies'){
foreach($value as $k=>$v){
$body .= $v.' ';
}
$body .= "\n";
}else{
$body .=$value."\n";
}
}
$body .= "\n";