The answer is "Euglena is an eukaryotic organism".
The main difference between prokaryotic cells and eukaryotic cells is presence of true nucleus and membraned organelles. Eukaryotic cells have true nucleus and membrane bound organelles such as chloroplasts, mitochondria, but prokaryotic cells have cyclic DNA instead of true nucleus and lack of membraned organelles. Euglena has a true nucleus and membrane bound organelles such as chloroplast. Hence, Euglena is classified as eukaryotic organism.