Are you meaning seeing what's hidden by dots when looking at a VPN config in the UTM Admin screen? If so, if you look at the page source when viewing the VPN configs, you can see the PSK in the clear.
If however, you are asking if you can find the PSK for an arbitrary VPN gateway where the admin hasn't told you it? In short, no. That's the point of a pre-shared key, it's supposed to be impossible to brute force.