What's are the variables can be used from content.field_name with multiple values I have created a field using test list type and rendering using custom twig code as below:

 {% for key, item in content.field_scope if key|first != '#' %}
    &lt;li class="item-list"&gt;{{ item }}&lt;/li&gt;
 {% endfor %}


In "for" argument, I manage to get value of key and item from the field. What are the other value which can be used?
{{ content.field_name }} is a renderable array. You are meant to simply print out {{ content.field_name }}.

If you need to change what is actually in the output, then you should create a field--field-name.html.twig or another applicable twig template suggestion name that works for you. Within it, you would have:

{% for item in items %}
  &lt;li class="item-list"&gt;{{ item.content }}&lt;/li&gt;
{% endfor %}


That way, any time you render either {{ content }} containing this field or {{ content.field_name }} it will use that template and render it consistently.

Here is a real world example. I am working on a project where one of the fields is a select list of about 20 options. These option values correlate to icons in the theme, and they can use this field to attach an icon to a title field for presentation purpose.

Here is my twig file for field--field-icon.html.twig:

{% for item in items %}
  &lt;svg class="icon"&gt;&lt;use xlink:href="/themes/custom/mytheme/build/img/svg-sprite.svg#{{ item.content }}"&gt;&lt;/use&gt;&lt;/svg&gt;
{% endfor %}


item.content is just my field value, you don't have to do anything special here. So if the editor selects 'Alert', which the select list value is 'alert', item.content will print alert and the proper icon will display from the svg spritesheet.

Here is a similar question I answered which may provide further insight on theming fields.