Find the graphics card with the laptop, most likely will be integrated graphics that comes with your CPU. Then search to see if that supports 4k monitor. The intel i5-4xxx processors do, for example, as Intel Graphics 4000 seems to support 4k.
I think the best approach is to ensure you're getting a latest-generation CPU, find one or more machines that you're considering, check which CPU or graphics they have, and google whether those specific machines/CPU/graphics options support 4k. Some machines are reportedly a bit flakey, some you'll find someone who has got it working just fine.