How do I find the source of water leaking though a wall?

Too many to count. Since it is raining, just bank it with old towels for now.

What is on the outside of the house? Landscaping? Concrete? Give us the lay of the land so we can come up with possibilities. My best guess without photos and any pertinent info, would be that rain water is draining toward your home instead of away from it, hence causing a leak and seeping.

Is there concrete, or something else either letting the water in or wicking it in? Could the water be coming in after running down the wall under the window, from the window leaking? I'm trying to describe inside the wall, basically. It would then come in where the floor meets the wall. Is the floor above a crawlspace that may be flooded? I would do some serious investigation while it's happening, to find the cause.

Assuming you've lived in this house awhile my best guess is the gutters are not draining correctly. Check to see if they are over flowing next to the house or if the downspout is pouring water out near the house.

Next, what worked for us, if the ground around your house is flat or level you may need to create a berm around the base of your house. We used dirt and mulch, mostly mulch. Just a thick layer raked up to the wall making like a ramp that directs rain away from the house. The mulch doesn't pull away when it gets dry so even after a very dry summer it will still keep the water away.

Hydrostatic pressure. Water finds the path of least resistance. When it rains the water table rises and is seeping through your foundation. You could need a french drain either inside or outside your foundation.

Haven’t live in house long, outside of where leak is is concrete. Just noticed leak this time around because of the heavy rain we had.

You may be able to insert self leveling sealant made by Sika or Dap between the concrete and the foundation until you can determine further action.

The concrete pad made have settled since installation.