In wordpress there can be more than one category. Thus it has to be kept in unordered list <ul> . The php command get_the_category() gives the array form of all the category. If you want to separate category by only comma you can do this
<?php
$category=get_the_category();
$separator=”, “;
$catall=”;
foreach($category as $cato){
$catall=$catall.”<a href=”.get_category_link($cato->term_id).”>”.$cato->cat_name.”</a>”.$separator;
}
echo trim($catall,$separator);
?>
If you have <ul> and <li> first of all enclose by <ul> with its class and put the code.
<ul class=”td-category”>
<?php
$category=get_the_category();
$catall=”;
foreach($category as $cato){
$catall=$catall.”<li class=’entry-category’><a href=”.get_category_link($cato->term_id).”>”.$cato->cat_name.”</a></li>”;
}
echo trim($catall,$separator);
?>
</ul>