Here is a list of features seen in all cells today: dna, rna, proteins, the genetic code, ribosomes, phospholipid membranes, dna polymerase for dna replication, rna polymerase, atp-ase (=atp synthase), reductive citric acid cycle..
from the above list, identify which ones are homologous in all cells today, and thereby candidates for being present in luca. one are more are not considered strong candidates for deep homologies in luca, but were rather 'invented' in independent lineages after luca.