You could use the Subset() function to "copy" cells to a new table. It's very versatile and allows for conditional row selection.
A column can also be copied by getting and evaluating its script. See the JSL examples of both approaches below.
dt1 = Open("$sample_data\big class.jmp");
dt2 = New Table("another table", New Column("data", values(1 :: 10)));
// Copy column "height" to another table (here from dt1 to dt2)
Eval(Eval Expr(dt2 << Expr(dt1:height << get script)));
//Or more direct: use Subset()
// "Copy" entire column(s)
dt_new = dt1 << Subset(Columns(height), All rows(1));
// Or copy conditionally
dt2_new = dt1 << Subset(Columns(height), Rows(dt1 << get rows where(height > 62)));
a