This D() result must be read in terms of the MuPad D partial-derivative operator. In that particular expression, it says, "Take the derivative of T2 with respect to the first parameter, then take the derivative of that result to the third parameter; then evaluate the result at the point where the first parameter has value dq1, the second has parameter dq2, the third has value p1(q2)
As your T2 does not appear to be defined as a function, it has had to proceed completely symbolically. Define T2 as a function at the symbolic level if you want to get any further.
For example,
T2 = sym('(x,y,z) -> x^3*(z-y/2)+y*z^2+5');
Then it would make sense to evaluate the Jacobian of T2 at the point (dq1, dq2, p1(q2))
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