A 3d plot is a good way to get an overall picture. 

plot3d(z,x=-1..1,y=-1..1,style=surfacecontour);

If you want specific z values for your contours, you can use the contours option:

plot3d(z,x=-1..1,y=-1..1,style=surfacecontour,contours=[-30,-20,-10,0,10,20,30,40]);

I think you wanted print(p) in B. But I agree there are no output plot files generated. (I'm using Maple 2015.) I usually use the interface command to do these plot outputs rather than plotsetup, e.g., interface(plotdevice=ps, etc), and maybe that is a clue. I'm guessing that since it is running headless, that means that none of those interface features work, and so plots cannot be output in this way.

You have 3 equations but have specified only one unknown. You should specify which three variables to solve for; then you will get these three in terms of the other variables. For example you get a solution with

solve({eq1, eq2, eq3}, {xk,xk1,xk2});

I would use implicitplot for this. I'm assuming z is a complex variable.

Download NonEuclideanLines.mw

To get RK4, use dsolve({IC, ODE}, numeric, method=classical[rk4], stepsize=h). See the help page ?dsolve,numeric.

Not sure exactly what you want to do, but you may find the singular command useful, which finds the singularities. You can add the option 'CauchyPrincipalValue' to an integral, e.g., int(1/x^3, x = -1 .. 2, 'CauchyPrincipalValue'). See the ?int,details help page. But as @vv points out, numerical integrals done like evalf(Int(...)) do not work with this option.

The problem is that Maple sees the " as the start of a string, but doesn't find the matching " at the end of the string, so thinks you aren't finished entering your command. You can enter `Trees_aren"t_pink`!; to solve this - this is the factorial of `Trees_aren"t_pink`; or if you wanted the ! to be part of the name then `Trees_aren"t_pink!`;
 

Your last line has add*rhs. Not sure what you want to do, but perhaps:
 

Download add.mw

Less for your stacking example, but generally useful is copy(vec) or LinearAlgebra:-Copy(vec), which makes a new copy of the vector (or rtable in general).

e has no special meaning, use exp(), and pi is Pi. (And that integral is definite, since it goes between specific values; I think you mean improper). Now it is fixed, hitting enter on that line executes it.

Download Integral.mw

You can use ListTools:-MakeUnique to remove the duplicates from a list.

Download Unique.mw

As @Sauberschrauber says, you probaby want exp rather than  "e", which is a symbol without special meaning. But you also have used "." for multiply rather than "*". There is unlikely to be an analytical solution.

Download solve.mw

I don't know why this would be - after all, 0.12 as an expression outputs as 0.12. If you care about exactly how the number is formatted, you can write it to a string using a format: sprintf("%f",0.12); gives "0.120000" and you can have fine control over number of digits etc by adjusting the format - see the help page ?sprintf.

I'm having the same issue (in Maple 2015). It seems you have to browse to a worksheet even if it is the open one with the bookmark in that you are editing. (I selected type worksheet and absolute path.) The help says you can leave it blank if it is the current worksheet, but this seems not to be the case.

A closer look with symbolic solutions finds more solutions but they all have x_2 = 20. But the equations already have some square roots which I assume need to lead to real solutions - perhaps this is not a valid assumption, or in leading up to these equations you have manipulated them in some way that precludes the solution you want. In particular is the other x_2 you want negative?
 

Download eqns.mw