In order to configure Twitter Cards Tags for Magento 2 Blog Post Page please go to Content > Blog > Posts and click on the post you're most interested in to start configuring.

Blog posts list

On the blog post page find the Twitter Cards Metadata section.

Blog post twitter cards metadata section

Twitter Cards Metadata

1. Set a Twitter Cards Title if you don't want Meta Title to be used instead. If it isn't set up the post title will be used.

2. In the Twitter Cards Description set the description of the twitter card. In case you haven't set it up the Meta description will be used. If none of the descriptions have been configured, the Default Description will be used.

3. Set the Twitter Cards Image, otherwise, Default Twitter Image will be used.

Blog post twitter cards metadata section

Once you've finished the configurations don't forget to press the Save Config button.

Twitter cards configuration save