Do the targets of Glasc Mixologist enter ready?

No, the targets of Glasc Mixologist do not enter ready.

According to its ability text, Glasc Mixologist's Deathknell allows you to "play a unit... from your trash, ignoring its cost." In Riftbound, playing a unit simply puts it onto the battlefield; it does not inherently include the "ready" action unless the card text explicitly states so.

Since there is no "ready" instruction in the card text, the unit will enter the battlefield in its default state (which is typically exhausted if it was put into play by an effect during a showdown or combat, or simply as is depending on the specific phase and game state).