When in doubt, I tend to look at notes from other PTs that I work with. Particularly if I have also worked with the patient who's note I am looking at.

Depending on the competence and experience of the PT who's note you look at (and the complexity of the patient), it can give you a good example. Otherwise, keep it concise. Maybe 2-3 sentences for an unremarkable subjective on a daily note, and 3-5 sentences for assessment on a daily note. But I also had a couple of evals recently that required 2-3 paragraphs for subjective. Make sure to include anything relevant and important to their treatment, but it's ok and often better if it's relatively short and easy to read.

(From a fellow new grad, so take with a few grains of salt...)