It should be the same as my 2017. It's the worst design I have ever seen. From under the passenger side dash, behind the glove box, there is a skinny cover - like 1" wide by about 8" tall towards the center. Once the cover is off, the filter slides out, new filter in. Then the fun starts - trying to get that cover back on. Helps to be skinny and flexible - which I am not. 2017 pathfinder cabin air filter location - Google Search
Just to add to the above. The CAF doesn't just slide out and in. The filter has to be collapsed to fit through the opening so the one coming out will often be destroyed in the process.
They are typically labelled with the direction of air flow, so be mindful of that. The new filter will need to be collapsed to fit it in and all you can do is hope it expands back to it's normal size once it's in there.
The access door for the CAF is in the passenger side footwell, about where the center console meets the firewall.
2017 .... I saw such posts and a good video on youtube as well. I expected a fight to get that cover back on, but I guess I was lucky and hit it first try. Took me all of 5 minutes to replace the filter in mine. A bright LED work light is helpful.