This example illustrates the basic steps. You could extend it in many ways to suit a particular case.
// set namespace
Names Default to Here( 1 );
// open data set
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
// launch platform and estimate parameters
biv = dt << Bivariate( Y( :weight ), X( :height ), Fit Line );
// obtain reference to report layer
biv rep = biv << Report;
// obtain p-value for parameter estimate from report layer
pVal = biv rep["Parameter Estimates"][NumberColBox("Prob>|t|")] << Get( 2 );