How do you practically measure brand awareness in B2B?

Agree on the top of funnel metrics - Organic web, SEO ranking vs. competitors, owned social channels.  For the PR portion of our tracking, we use a tool called Meltwater to track our monthly press mentions and total press outreach.  It has been a big help in demonstrating the value of PR activity.  In my experience, brand surveys are pricey and often give skewed data as it can be hard to target your audience well (especially in niche B2B products).

As a first step, we've created our internal tracker which incorporates direct website traffic, branded searches (we get through a tool), social media engagement (followers we get and LI engagement rate), press & AR coverage. Next thing will be to pay for a brand tracker (aided and unaided recall, brand sentiment).

Agree with Gary and Url but I would also include Share of Voice, backlinks, branded search volume/traffic and an increase in branded keywords. 

My company measures brand awareness in a number of ways -- namely through Google search analytics, web traffic, media exposure, and analyst inquiries. I don't think there is one single metric that can encapsulate something as broad as brand awareness. You need to measure all these things to get a full picture and identify key trends.