d|v| /dt means the rate of change of magnitude of velocity with respect to time. On the other hand |dv/dt| means the magnitude of rate of change in velocity with respect to time (i.e. the magnitude of acceleration).
Lets take an example:
A body was travelling at 5m/s along the positive x-axis. Its velocity changed to 3m/s along negative x- axis in 1 second.
Here ,
d|v|/dt = (3 - 5)/1
= -2m/s^2
|dv/dt| = (-3 - 5)/1
= -8m/s^2
Hence these both cannot be equal.