how to define variable in yii2 param

Set variable:

Yii::$app->params['abc'] = hemant;

Get variable:
echo Yii::$app->params['abc'];

how to define variable in yii2 param

Facebook Object Debugger: property 'og:url' could not be parsed as type 'url'

You should have scheme in front of og:url content (like http:// or https:// ), or this isn't URL.

In your specific case you should replace www.hemant9807.blogspot.com/testobject with http://www.hemant9807.blogspot.com/testobject

How to get url of current wordpress theme?

<?php echo get_template_directory_uri(); ?>

How to get url of current wordpress theme?