I don't know of any laptop that actually has a fully fledged standard PCI/PCIe slot in it and for good reason, it would defeat the purpose of a laptop. Some laptops do have a GPU housed on a separate and removable module that plugs into a customised PCIe slot on the motherboard of the laptop, but there are very few of these kinds of systems, and even fewer choices when it comes to what GPU's can actually go in them.
However you may be in luck. If your laptop has a thunderbolt connector you may be able to connect an externally housed GPU to it and its only a may because some manufacturers implementations will still not support an e-gpu. While Thunderbolt only exposes a very limited number of PCIe datalanes it could still detect the card and allow you to use it albeit at significantly reduced performance.
In short Gam3r01 is quite right, you'll need to look at the specification of your laptop and assuming it has a thunderbolt port you will then need to research a suitable e-gpu that you can connect to it. Just bear in mind that if you do find one you will still not be able to leverage the full capabbility of the GPU, don't go and buy a 1080 e-gpu for example because you'll be wasting your money on a device whose features you can't leverage.