I am not sure if this solution is like a more more detailed list of things to try to solve the problem. If you notice a problem with any of these things, it can narrow your search down to what's going on.
Have you tried the option by clicking to see if this really brings you to the file? Sometimes Xcode will complain that it does not exist, but this is paradoxical for you when you try to click an option. This can be hoped to be solved without resorting to discussing the linking / search paths, which I will discuss below, but removing the project and more.
But at the same time, the first course of action with this should always be to clear the project (Product> Clear) and close Xcode again in order to try to find out if it resolved automatically. You can also try holding down the Option key after clicking on "Product", and the "Clear" option will change to "Clear the assembly folder", which will delete all the intermediate and assembly files and something else.
Similarly, you can also try to clear the Derived Data folder (Xcode> Preferences> Locations>) by clicking the arrow next to the "Derived Data" folder).
Another stupid mistake that can lead to this is opening the .xcproj file instead of the .xcworkspace after installing Cocoapods.
Now, assuming this doesn't work, you'll probably want to make sure Cocoapods have everything connected correctly. If you go to your build settings and click "Goal": 
You want to make sure libPods-YourProject.a is in the Linked Frameworks and Library section (you will probably get a few other errors if this is not the case, but I just mentioned it to be complete). If this is not the case, then some strange problem with Cocoapods and me will probably recommend installing pods again or uninstalling and adding Cocoapods to your project.
Similarly, if you now click "Build Settings" and scroll down to "Binding", the "Other Linker Flags" option will appear. Make sure there is a flag on which the flags are set: $ (inherited). As part of this, Cocoapods was supposed to add a bunch of flags that start with -l "PodName". Now I'm not 100% positive, because you have header files in addition to the additional frameworks folder, but what I think you need to see is l "Google" and then under all the flags -l "name" you You will see an additional two linear flags:
Make sure there is one that says the "GGLCore" framework
Now you also probably want to check your search paths. Therefore, still in the "Build Settings" section, scroll down the page until you find the "Search Paths" options. Make sure you have search paths in the Framework, there is also $ (inherited), and you should see explicit search paths on the right (not when you click on it for editing, there you will only see $ (inherited).
More important, however, is the section under the headings of the heading search. If you click on it, you will see a bunch of options that look something like this: "${PODS_ROOT}/Headers/Public/NameOfPod" to put Google back on this list. If you open your project in a search device (right-click on Pods and click "Show in Finder"), you can also explicitly go to the header files by going through Pods> Headers> Public).
Most likely, where everything goes wrong, and there is an existing question about stack overflow, you can find here , which can give you several other suggestions on what to do.
Not entirely positive if it is recommended, but if you find the location of the header that you are trying to import, you can try explicitly adding it to the "User Header Search Paths", which is located at the bottom of the search path parameters you are looking at.
My suggestion to you, however, if you find that something strange in this regard is to uninstall and reinstall Cocoapods, as this should take care of you by them. And by that I mean Cocoapods completely de-integrated