  The diffuse ionized gas (DIG) is an important component of the interstellar
medium and it can be affected by many physical processes in galaxies. Measuring
its distribution and contribution in emission allows us to properly study both
its ionization and star formation in galaxies. Here, we measure for the first
time the DIG emission in 38 gas-stripped galaxies in local clusters drawn from
the GAs Stripping Phenomena in galaxies with MUSE survey (GASP). These galaxies
are at different stages of stripping. We also compare the DIG properties to
those of 33 normal galaxies from the same survey. To estimate the DIG fraction
(C$_{DIG}$) and derive its maps, we combine attenuation corrected H$\alpha$
surface brightness with $\rm [SII]/H\alpha$ line ratio. Our results indicate
that we cannot use neither a single H$\alpha$ or $\rm [SII]/H\alpha$ value, nor
a threshold in equivalent width of H$\alpha$ emission line to separate spaxels
dominated by DIG and non-DIG emission. Assuming a constant surface brightness
of the DIG across galaxies underestimates C$_{DIG}$. Contrasting stripped and
non-stripped galaxies, we find no clear differences in C$_{DIG}$. The DIG
emission contributes between 20\% and 90\% of the total integrated flux, and
does not correlate with the galactic stellar mass and star-formation rate
(SFR). The C$_{DIG}$ anti-correlates with the specific SFR, which may indicate
an older ($>10^8$ yr) stellar population as ionizing source of the DIG. The DIG
fraction shows anti-correlations with the SFR surface density, which could be
used for a robust estimation of integrated C$_{DIG}$ in galaxies.
