How would I go about tracking the current speed of a sprite on the x axis?

What do you mean?

Here's a very simple velocity script:

when flag clicked
set [x velocity v] to [0]
go to x:[0] y:[0]
forever
if <key [left arrow v] pressed> then
change [x velocity v] by [-1]
end
if <key [right arrow v] pressed> then
change [x velocity v] by [1]
end
change x by (x velocity)
set [x velocity v] to ((x velocity)*(0.9))
end

I want to measure the current speed a sprite is moving left or right

0.9 is a friction value (how fast it slows down - the closer to 1, the slower it decelerates, the closer to 0, the faster it decelerates)

Yes, and in this script, that would be x velocity.
If, for example, x velocity is -5, that would mean the velocity to the left is 5. If x velocity were 8, it would mean the velocity to the right is 8.

This is a good movement script however what I want is to track the speed of a sprite on the x axis, not to create a fluid movement script.

What do you mean speed? Here, x velocity is the speed. Can you show me an example? (for example the project you need this for)?

Do you just mean how much it moved left or right each frame?

The script you provided is changing the x velocity directly, however the script I want is to measure the x velocity at which a sprite is currently moving without messing with the movement of a sprite.

yes, how much it moves left/right

That isn't technically x velocity. But if that's what you are looking for, then try this:

when flag clicked
forever
set [x movement v] to ((x position)-(old x position))
set [old x position v] to (x position)
end

Yes that works thanks.

No problem!

also guys if u want the speed of the x to go to only 6 the you set the part on the set velocity x to .8571428599