I have placed the code on:

loop-grid
loop-list
loop-search-grid
loop-search-list
loop-user-alerts-grid
loop-user-alerts-list
loop-user-grid
loop-user-list
loop-user-public-grid
loop-user-public-list

However, the Favorite Button doesn't appear on my Home Page and on my Dashboard (My Listings). Grid is not showing well but List is. And how do I change the Favorite Button for the List to go inside the Box instead of outside? For the Grid, I would like it to be inside also.

Please see the screenshot:
Dashboard (My Listings) List http://prntscr.com/9mco9j

Dashboard (My Listings) Grid
http://prntscr.com/9mcoh6

Home Page List
http://prntscr.com/9mcoo1

Home Page Grid
http://prntscr.com/9mcouf

Search Page List
http://prntscr.com/9mctjj

Search Page Grid
http://prntscr.com/9mctqr

My Website is https://cheapy.sg. Thanks.

@Cheapy
1) On homepage this button does not exist, it means it was place outside listing loop or in incorrect file, communicate with your theme developer

2) Placing this to user alert loop or user list/grid does not give any sense, as only user that has posted those listings can make them favorite from those pages, so does not do it on those pages

3) On search page code is entered on incorrect place outside <li></li> tags.
In code you have sent before you would place it not like this (INCORRECT):
//latest items
if($type == 'latestItems'){
$listcount = 0;
echo '<ul class="isotope row">';
  while ( osc_has_latest_items() ) {
                echo fi_make_favorite();

?>
  <?php $size = explode('x', osc_thumbnail_dimensions()); ?>
  <li class="item listing-card col-sm-6 col-md-<?php echo $cols;?> <?php if(osc_item_is_premium()){ echo ' premium'; } ?>">
    <div class="figure">
      <figure>
        <?php if( osc_images_enabled_at_items() ) { ?>
        <?php if(osc_count_item_resources()) { ?>
        <a class="listing-thumb" href="<?php echo osc_item_url() ; ?>" title="<?php echo osc_esc_html(osc_item_title()) ; ?>"><img src="<?php echo osc_resource_thumbnail_url(); ?>" title="" alt="<?php echo osc_esc_html(osc_item_title()) ; ?>" width="<?php echo $size[0]; ?>" height="<?php echo $size[1]; ?>" class="img-responsive"></a>
        <?php } else { ?>

but in this way (CORRECT):
//latest items
if($type == 'latestItems'){
$listcount = 0;
echo '<ul class="isotope row">';
  while ( osc_has_latest_items() ) {

?>
  <?php $size = explode('x', osc_thumbnail_dimensions()); ?>
  <li class="item listing-card col-sm-6 col-md-<?php echo $cols;?> <?php if(osc_item_is_premium()){ echo ' premium'; } ?>">

    <?php echo fi_make_favorite(); ?>
    <div class="figure">
      <figure>
        <?php if( osc_images_enabled_at_items() ) { ?>
        <?php if(osc_count_item_resources()) { ?>
        <a class="listing-thumb" href="<?php echo osc_item_url() ; ?>" title="<?php echo osc_esc_html(osc_item_title()) ; ?>"><img src="<?php echo osc_resource_thumbnail_url(); ?>" title="" alt="<?php echo osc_esc_html(osc_item_title()) ; ?>" width="<?php echo $size[0]; ?>" height="<?php echo $size[1]; ?>" class="img-responsive"></a>
        <?php } else { ?>

Than you can apply custom CSS styles on element:
.listing-card .fi_make_favorite {}

Removed

loop-user-alerts-grid
loop-user-alerts-list
loop-user-grid
loop-user-list

Do I need to remove
loop-user-public-grid
loop-user-public-list

As well?

Also what do I need to write inside CSS? Thanks.

@Cheapy
Following two:
loop-user-public-grid
loop-user-public-list

belongs to user public profile. It is on you if you want to have button there...

In CSS you write custom styles if you need it, especially positioning....
http://www.w3schools.com/css/

Okay, can you help me with positioning by giving the Code? Thanks.

@Cheapy
You can do it by yourself.
Add to style.css code:

.listing-card .fi_make_favorite {
  position: absolute;
  top: 10px;
  right: 10px;
}

You can play with above code changing 10px to value you need.