For the sake of others I retrieved the details using this code:
import tensorflow_datasets.core.dataset_builders.conll.conllu_dataset_builder_utils as conllu_utils
from tensorflow_datasets.core.features.class_label_feature import ClassLabel
UPOS = conllu_utils.UPOS
upos_mapping = ClassLabel(names=UPOS)
print(upos_mapping.int2str(5))