"part of speech" - "sanaluokka"
If you want to try asking about this in the future, in Finnish, you can say e.g.: "Minkä sanaluokan sana x on?"
"Sujuva" (sing. part. "sujuvaa") is a present participle, that is, a verb that resembles an adjective. It's derived from the verb "sujua", which is a bit hard to translate but can be found in sentences such as "Miten sujuu?" (How is it going?), "Sujuuko kaikki suunnitelman mukaan?" (Is everything running/going according to plan?) etc. Other participles introduced in this course include at least "syötävä" (syödä) and "juotava" (juoda).