Short answer: everything related to technology. Of course, the focus of different technology blogging jobs would depend on the company who offers them.
For instance, if the company wants tech news for their company blog, and they focus on eco-friendly or "green" technology like alternative power sources, then they would typically cover news about advances in green technology. You could also expect feature articles, opinion or editorial style pieces, and perhaps a few reviews or analyses of issues or developments that directly concern them. Technology companies and websites often focus on a wide range of technology related topics, however, not just a single niche.
It is also common to see a website focusing on one topical subcategory and branching out to related fields. A video game website could branch out to gaming technology that covers topics on platforms, mobile devices that offer the best gaming experiences for casual and / or hardcore gamers, and so on. It's almost inevitable that most technology topics are closely related to one another. Given this situation, successful websites either cover almost all technology related topics if they can, or just focus on one topical category and cover other stuff that's relevant.
A good example of the first one is CNET technology news. In their news categories, major brands Apple and Microsoft are included among umbrella categories like Gaming & Culture, Mobile, Cutting Edge, and Health Tech. Figuring out how to categorize topics in a fashion that provides target readers the best coverage of the concerns and issues most relevant and significant to them can be challenging, and as you can probably tell from the categories on CNET, some news or articles could fall under several general categories at once.
A good example of a niche site that branches out is a site called CapsuleComputers.com.au - they focus on video games, but also cater to some tech culture topics, and even some popular culture ones like anime and manga. From the content on their website, it's easy to tell that there's a ton of news in just their field of focus - video games and gaming. So compared to their main thrust, popular and tech culture articles are limited.
Looking at how such sites are set up, if you go for technology blogging jobs you can expect to either be assigned (or made to choose which) topical subcategories to write about, or be tasked specific functions. Being responsible for a wide range of topical subjects is challenging because of the variety of topics. Being tasked to write about one specific topic is challenging because of the depth you probably need to incorporate into your work. But we're talking about blogging jobs here - you may occasionally write a heavy-hitter or two, but for the most part you will still be writing blog posts. So long as they add value to the reading experience of the target audience, then it's all good.
The topics technology blogging jobs cover can be everything related to tech, but most probably you'll be writing about specific topics within the vast technology field.