how to add logo to navigation bar in twenty eleven?

In the centre of the menu?

yes, like
about faq uuu LOGO xxx xxx xxxx

I think the only way you’ll be able to do this is by creating a custom menu and then using the Custom Url option to add your link to the menu. Then you can use CSS to add the logo image as a background to that link. But do not edit the Twenty Eleven theme. It is the default WordPress theme and having access to an unedited version of the theme is vital when dealing with a range of site issues. First create a child theme for your CSS additions.