Direct link to composing a comment?

[simon]

@haydenjames

If a topic is located at:

discourse-forum(dot)com/t/topic/123

Is it possible to create a link that automatically opens the reply box when clicked?

This is not possible. You can create a link that automatically opens the post editor for a new topic, but you cannot create a link that functions in that way for replies to an existing topic. Details about creating links for new topics are here: Create a link to start a new topic with pre-filled information.