The @transform syntax is only valid in Code Repository, when writing Python transforms. https://www.palantir.com/docs/foundry/code-repositories/create-transforms

You can read/write datasets in Code workspace (Jupyter CodeNotebook flavor) with another syntax See https://www.palantir.com/docs/foundry/code-workspaces/data/#tabular-datasets

from foundry.transforms import Dataset

kittens = Dataset.get("kittens")\
  .read_table(format="arrow")\
  .to_pandas()