As mentioned in the other answer, https://docs.joomla.org/J3.x:Adding_custom_fields/Overrides is the key description to understand. To quote:
Basically you have all the custom fields corresponding to the current item accessible via a new property in your $item variable called jcfields.
and that Joomla documentation page lists all the fields of the ...
What you try to achieve is this. I point you to an quick snippet to point you to the right direction. Here it is.
defined('_JEXEC') or die;
<ul class="list-group list-group-flush">
<?php foreach ($list as $item) : $image = json_decode($item->images); ?>
// most important part
I have never used DPCalendar, so your mileage may vary, but I've had some luck tinkering with getting custom fields in overrides like this:
n in this example is the array position of the desired custom field. Raw value retrieves the data.
Here is a nice explanation in the Joomla documentation.