You could export the plot and then open it in an external application.
$ wolframscript
Wolfram Language 12.0.0 Engine for Mac OS X x86 (64-bit)
Copyright 1988-2019 Wolfram Research, Inc.
In[1]:= f[x_] := Sin[x^2]
In[2]:= Export["plot.png", Plot[f[x], {x, -Pi, Pi}]];
In[3]:= !open plot.png
On Windows, replace open with whatever application you want to use to open the png file.
