Minecraft – why does the scoreboard not work

Your command blocks are placed in the wrong order in the world.

When multiple command blocks are powered at the same time, they are executed in the direction of +X, +Y and +Z. It is very likely that your line of redstone "points" in the -X or -Z direction, thus making the game run the commands in reverse order:

/execute @e[score_Holding_min=1] ~ ~ ~ /summon LightningBolt ~ ~ ~
/scoreboard players set @a Holding 1 {DataTag}
/scoreboard players set @a Holding 0

This leaves every players Holding score at 0 at when the execute command is run, therefore it does not execute properly.

In 1.9+, chain command blocks should be used to easily prevent such issues.

You can use scoreboard in player selectors to find out which one they clicked. Usually this is done by either testfor or execute.

I recommend a 20 t/s clock to check these as soon as they click it. You don't have to use one, but it may help. great method to setup one.

In the case of testfor, it is actually not recommended to use it. You can't exactly distinguish which player clicked it, you just know that it was clicked. A better way is the execute method. Never-the-less, the command should look like this:

Testfor @a[score_test=1,score_test_min=1]

You will need a comparator to get if it succeeded to find it. You should also have a separate command block for each, then change the 1 to another number for each possible outcome.

In the case of execute: recommended method. You can use @p in the command part to target that specific player. Command as follows:

Execute @a[score_test=1,score_test_min=1] ~ ~ ~ <command>

For this, you should set their score of that to 0 as soon as the command is run, otherwise that command may be run twice.