IR Spectroscopy
In alkenes, the C-H stretch will be to the left of 3000. The C=C stretch appears as a medium band from 1680-1640.
NMR Spectroscopy
Alkene protons show up from 4.65.9 ppm. If the system is conjugated, they are shifted to 5.57.5 ppm.
A benzylic-conjugated proton (example below) can show up in the aromatic region.
Example