Graph of tan(x-[x])?

Whatever x is, (x-[x]) will always lead to 0.
Therefore (x-[x])=0
So replace (x-[x]) by zero in the equation tan(x-[x]), you will get tan(0).
The answer of tan(0)=0
But to graph the equation you need x and y.
So in this case tan(x-[x]) is y, and since the answer is always 0 therefore y=0
So the points will be (x,0) where x belongs to all real numbers.

To sum up, the graph will be a straight horizontal line coinciding with the x-axis; in other words, the graph is the x-axis itself.

I hope its helpful.