pathfinder 1e – Can the spell Shocking Grasp damage more than one target at the same time?

As raw, Fering answer it.

I would like to add another point. Lets the see, in your own homerule table.

As a DM, I will allow it. I will allow it, because I do not want to see my players hampered by the rules. Rules are here to support the game, not to limit it.
I want to see them thinking out of the box. I want them to think and show creativity. Your case is a borderline move, but a logical and out of the box one. By rewarding them, I send a message. Do it more!

It is like the question of using Grease with fire.

Also, this kind of move can bring unbalance to the game. As which each unbalance problem, you will have to handle it. Basically, you are not saying “No”, you are saying “Yes, but”.

For example, a nd6 Shocking Grasp could become $frac{n}{2^x}timestext{d}6$ where $x$ is the iterator of the target. Each target become a kind of resistance.

So for 3d6, $frac{3}{2^0}timestext{d}6 = 3text{d}6$ for the first target, then $frac{3}{2^1}timestext{d}6 = 1text{d}6$ for the second target, then $frac{3}{2^2}timestext{d}6 = 0text{d}6$ so nothing for the third one.

Another kind of rule could be to split the damage and each target take half the damage each time (8d6 = 4d6 + 2d6 + 1d6 + 1d6 or 3d6 = 2d6 + 1d6). You could even add modifiers (bonus or malus) for whatever.

Demo: Scamage (build it myslef. Any input is welcome :3)

Caster tends to be top tier. Be careful with balance. Find one logic for your table and go for it. We are here to have fun.