after being hit by an ion cannon can a ship use a combat action ? are combat actions different to planning actions

Being hit by an ion cannon does not keep you from spending focus, evade, or target lock tokens or otherwise benefiting from previously taken actions (like marksmanship). Note that there is no such thing as "combat actions" and that marksmanship must be used as your action earlier in the round.

can i use marksmanship if i am touching a ship and target another

wormiespice said:

If you collided as a result of your movement, then you lose your action and cannot use marksmanship. If you end your movement not touching any ship, you can use marksmanship at that time. You can then apply the benefit to any attacks you make that round, but the attacks themselves still have to be legal (can't attack a ship touching you).