During the Spanish invasion in Iraq (2004) did Iraq hold any Spanish POW or viceversa?

No. The Spanish government sent a small force that did not actually engage the Iraqi Army during the period before the government fell. Even among the British and Americans, who did almost all of the fighting, there were virtually no prisoners of war taken by the Iraqis. They were too busy running away to take prisoners. Similarly, because the Spanish did not engage the Iraqi military, they did not take prisoners of war. There may have been some prisoners taken after combat operations ended, but they were turned over to the Americans or the British. The Spanish did not maintain a sufficiently large military presence to keep prisoners.