Our company wants to do session collaboration with people who don't work for this company(They are not connected to our domain). can we do that from Qlikview Ajax Client? or Do we need any external server?
You would need to configure an external facing server. The customer needs to have access to your network for session collaboration to work correctly. It's worth taking with your Account Manager to see how they can help you, deliver a solution to your customers.
You'll need to talk with your Account Manager (you'll need to discuss removing the limitation for session collaboration within Extranet Server). You'll be able to choose from Session Cal's and Usage Cals as licensing options for your customer's or partner's, when using Extranet Server. You'll be able to share up to 3 QlikView documents/applications.
Extranet Server (is QlikView Server with license limitations) therefore, you will not find an Extranet Server download or install guide, Use QlikView Server Enterprise Edition documentation.