Short of the possibility that you are reading someone else's bad writing,
$$\frac{d}{dx}(e^x)^2+6 = 2e^{2x}+6 \
eq \frac{d}{dx}\left((e^x)^2+6\right) = 2e^{2x}.$$
Mathematical notation is supposed to be quite unambiguous, and so I would not differentiate the constant unless I knew that the author was just being sloppy and really intended the latter.
The differential operator $\frac{d}{dx}$ distributes over addition just like scalar multiplication, and so these parentheses are quite necessary if it is the author's intention to differentiate the 6.