I'm assuming you mean you don't know if your dynamic table always has the column you're looking for.
Use the Runtime Type Services (RTTS) to determine the structure of the dynamic table. The following bit of data will determine if your structure has a field called 'NUMBER'. You can use table lt_component to check which component you need to read ( ASSIGN COMPONENT number OF STRUCTURE <fs_line> TO <fs_field>
).
DATA:
lr_tabledescr TYPE REF TO cl_abap_tabledescr,
lr_datadescr TYPE REF TO cl_abap_datadescr,
lr_structdescr TYPE REF TO cl_abap_structdescr,
lr_typedescr TYPE REF TO cl_abap_typedescr,
lt_component TYPE TABLE OF abap_componentdescr.
DATA tab TYPE TABLE OF sflight.
lr_tabledescr ?= cl_abap_datadescr=>describe_by_data( tab ).
lr_typedescr ?= lr_tabledescr->get_table_line_type( ).
lr_structdescr ?= lr_typedescr.
lt_component = lr_structdescr->get_components( ).
READ TABLE lt_component WITH KEY name = 'NUMBER'.