I found that the documentation to create a blog and wiki is not clear in IBM WebSphere Portal Infocenter. Here are the basic steps to create a wiki in Portal.
1. Login to Portal as Administrator. Go to Administration, Under Portal User Interface -> Manage pages. Drill down to Home. Under Home create a page MyWiki with layout as single column. Save the changes.
2. Now, go to location - Home - MyWiki.
3. Switch Edit mode ON
4. click on Create - Content - Select wiki and then click - Add to page button found at the corner. A wiki is created.