You should try to speak to a trend that is related to the group you’re interviewing for or the subsectors that the PE firm focuses on. For example, if the group is focused on infrastructure, you can speak to how solar power projects have been significantly boosted from the US infrastructure spending bill, and many states are experiencing an all-time record in terms of infrastructure projects.
You should also look at their recent deals and portfolio companies and try to pick a trend that applies to these deals / companies. For example, if the firm is focused on a very specific sector of healthcare, like dentistry, then it would be ideal to pick a trend that is affecting that specific subsector. In dentistry, a common trend is that private equity firms are buying smaller family practices and rolling them up into a bigger platform. This allows the owners to cash in on their business, but it also helps the practice gain efficiencies of scale by applying best practices to IT and accounting so the dentists can focus on their core jobs rather than worrying about accounts receivables.
You can also look at similar deals done by other PE firms and speak to how this is part of a larger trend or theme in the PE world.
If the PE group you’re applying to is a generalist group or industry-agnostic, then take a look at their recent deals and portfolio companies and choose a trend that affects one of their investments.