Most mock drafts have the Chargers taking a quarterback with the sixth pick. Other drafts have offensive linemen. The common selections you’ll see at six in most recent mock drafts include the likes of Justin Herbert and Jordan Love at quarterback. Other drafts want the Chargers to bolster the offensive line in the first round, with picks like Jedrick Wills and Andrew Thomas.
For full disclosure, my belief at the moment is that the Chargers will select Herbert with the sixth pick. My most recent mock draft went into more detail on that.