Question: I want to include SFDC Knowledge Icon on VisualForce Page .
Some of the icons URLs could be found [HERE](http://free-121d5f44d20-121d603d1c5-121ee2b8103.force.com/force2b/salesforceicons)
But URL knowledge Icon is not specified here.
Whats the URL for Knowledge Icon?

Answer: 
To see the tabs, you need the 'Knowledge User' permission after enabling Knowledge itself. This avails the 'Articles' and 'Article Management' tabs, then we can find the icons living in their own folder:

1. Knowledge icon:

	* [/img/knowledge/knowledge16.png](https://login.salesforce.com/img/knowledge/knowledge16.png) (16px) ![knowledge128](https://i.stack.imgur.com/GKdBv.png)
	* [/img/knowledge/knowledge24.png](https://login.salesforce.com/img/knowledge/knowledge24.png) (24px) ![knowledge128](https://i.stack.imgur.com/uUQge.png)
	* [/img/knowledge/knowledge32.png](https://login.salesforce.com/img/knowledge/knowledge32.png) (32px) ![knowledge128](https://i.stack.imgur.com/lxWdQ.png)
	* [/img/knowledge/knowledge64.png](https://login.salesforce.com/img/knowledge/knowledge64.png) (64px) ![knowledge128](https://i.stack.imgur.com/3pcDg.png)
2. Knowledge management icon

	* [/img/knowledge/publishing/knowledgemanagement16.png](https://login.salesforce.com/img/knowledge/publishing/knowledgemanagement16.png) (16px) ![knowledge128](https://i.stack.imgur.com/405ap.png)
	* [/img/knowledge/publishing/knowledgemanagement24.png](https://login.salesforce.com/img/knowledge/publishing/knowledgemanagement24.png) (24px) ![knowledge128](https://i.stack.imgur.com/NTRIE.png)
	* [/img/knowledge/publishing/knowledgemanagement32.png](https://login.salesforce.com/img/knowledge/publishing/knowledgemanagement32.png) (32px) ![knowledge128](https://i.stack.imgur.com/WnhCo.png)
	* [/img/knowledge/publishing/knowledgemanagement64.png](https://login.salesforce.com/img/knowledge/publishing/knowledgemanagement64.png) (64px) ![knowledge128](https://i.stack.imgur.com/T1w4q.png)
Something like: 
<https://cs5.salesforce.com/img/knowledge/knowledge24.png>

but I would advice you to upload the image as a static resource