You can use Join/Update or Data table subscripting . Below is one example using update which might work for you
Names Default To Here(1);
// Setup demo
dt = Open("$SAMPLE_DATA/Trial1.jmp");
dt2 = Open("$SAMPLE_DATA/Little.jmp");
dt << Delete Rows(5 :: N Rows(dt)); // to make tables equal in size
Column(dt2, "batch") << Set Name("B"); // names must be different
Column(dt2, "yield") << Set Name("Y"); // names must be different
Wait(0);
collist = dt2 << Get Column Names("String");
lastcols = Right(collist, 2);
dt << Update(
With(dt2),
Add Columns from Update Table(Eval(lastcols)),
Replace Columns in Main Table(None) // important
);
-Jarmo