You can use a Where statement to filter by a specific value. If you are adding a Where clause to a script that contains column references, you must first resolve the references. The following example limits the analysis to females and fits a line on the Bivariate report.
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
Ycol = Column( "weight" );
Xcol = Column( "height" );
biv2 = dt << Bivariate(
Y( Ycol ),
X( Xcol ),
Fit Line( ),
Where( :sex == "F" ) );