If you are not sure as to the structure of the table prior to executing a program then you need to define the table dynamically - Here's how you do it...
types : begin of itab,
vbeln type vbrk-vbeln,
end of itab.
data : itab type standard table of itab.
data : wa type itab.
data : obj1 type ref to data,
obj2 type ref to data.
field-symbols : <fs_table> type any table,
<fs_line> type any,
<fs_field> type any.
* Example internal table
wa-vbeln = '123'.
append wa to itab.
*Create a DATA object like ITAB.
create data obj1 like itab.
* Assign the structure of ITAB to the field-symbol <FS_TABLE>.
* <FS_TABLE> now has a table structure
assign obj1->* to <fs_table>.
if <fs_table> is assigned.
* assign the values if ITAB to the field symbol <FS_TABLE>
<fs_table> = itab[].
* in order to read the contents of the table, we need a work area.
* So we create a data object which has the same structure as line of
* ITAB and then assign it to <FS_LINE>.
create data obj2 like line of <fs_table>.
assign obj2->* to <fs_line>.
loop at <fs_table> assigning <fs_line>.
* in order to access the individual fields of the work area we will
* have to use the Assign Component statement.
* This component can be either named if we know the fieldname or we
* can give the column position
assign component 'VBELN' of structure <fs_line> to <fs_field>.
* or ASSIGN COMPONENT 1 OF STRUCTURE <fs_line> TO <fs_field>.
if <fs_field> is assigned.
write <fs_field>.
endif.
endloop.
endif.