Use the knocking method.
How to find a stud in the wall by knocking, this we will discuss below.
How to Find a Stud in the Wall by Knocking
One of the best methods on how to find studs without a stud finder is by knocking. Knocking is the simplest and quickest way to find a wall stud and also one of the most reliable ways if you’re not into using any electronic tool. However, experts suggest that to have a more reliable way to find the position of the studs, you must knock on each side of the wall and listen for that deep solid sound and measure both the wall’s corner to where studs are assumed to be.
Here are the knocking procedures: 
Always find your starting point.
As discussed above, your starting point or base for measurement could be the electrical outlets or switches, trims on baseboards, and also corners or windows. To use windows, since all windows will be supported by studs, there will always be studs that you can find on either side of them.
For corners, remember that all wall structures need to be fixed on a stud and you could easily find a stud on the corner of a wall. Once you have found the stud on a corner, this can be your starting point on how to find studs without a stud finder using only the knocking method. 
Knocking on the wall.
The technique in using the knocking method is by using your knuckle and bringing your ear near the wall and listening for that dense sound. From hollow to deep solid sound, this can strongly indicate a stud behind the drywall. You can also use a plastic cup and stick its mouth into the wall while your ear is pressed at its bottom then knock. As you hear the solid sound, mark it with tape or a pencil. From here, you will know if the studs’ distances are 16 or 24 inches away.