Sometimes these questions are posed in relation to cells and sometimes as test tube reactions: such as ‘will some substance oxidise another substance’. The simple memory aid regarding cells is that the anode is where oxidation takes place.
Regarding test tube reactions the convention is to write both the half reactions as reductions and the most positive will go to the right i.e. will be the forward reaction.
This should help you work out specific examples for yourself or at least have a go at showing your own attempt before asking for further help.