Any Legion Centurion may select a single Consul upgrade; no model may take more than one such upgrade. The various Consul types are listed here, but full rules for them can be found in the appendix Legiones Consularis on page 104: 
Centurion (pg 22)
Universal: Librarian (Not White Scars), Esoterist, Master of Signals, Champion, Forge Lord, Primus Medicae, Siege Breaker, Chaplain, Vigilator, Pathfinder, Moritat, Praevian, Delegatus, Herald, Armistos, Mortifactor & Warmonger (Legacies Download).
Legion Only: Paladin of Hekatonystika (Dark Angels), Stormseer (White Scars), Pack Thegn (Space Wolves), Speaker Of The Dead (Space Wolves), Caster Of Runes (Space Wolves), Castellan (Imperial Fists), Warsmith (Iron Warriors), Dark Emissary (Sons of Horus), Diabolist (Word Bearers) & Saboteur (Alpha Legion)

Cataphractii Centurion (pg 24)
Universal: Librarian (Not White Scars), Esoterist, Champion, Forge Lord, Primus Medicae, Siege Breaker, Chaplain, Delegatus, Herald, Mortifactor, Primus Nullificator (Legacies Download) & Warmonger (Legacies Download).
Legion Only: Paladin of Hekatonystika (Dark Angels),  Stormseer (White Scars), Pack Thegn (Space Wolves), Speaker Of The Dead (Space Wovles), Caster Of Runes (Space Wolves), Warsmith (Iron Warriors), Dark Emissary (Sons of Horus), & Diabolist (Word Bearers), 

Tartaros Centurion (pg 25)
Universal: Librarian (Not White Scars), Esoterist, Champion, Forge Lord, Primus Medicae, Siege Breaker, Chaplain, Delegatus, Herald, Mortifactor.
Legion Only: Paladin of Hekatonystika (Dark Angels), Phoenix Warden (Emperor's Children), Stormseer (White Scars), Pack Thegn (Space Wolves), Speaker Of The Dead (Space Wolves), Caster Of Runes (Space Wolves), Warsmith (Iron Warriors), Dark Emissary (Sons of Horus), & Diabolist (Word Bearers).

Used By (3)

(HH V2) Legions Astartes/Centurion(Entry)

(HH V2) Legions Astartes/Centurion, Cataphractii(Entry)

(HH V2) Legions Astartes/Centurion, Tartaros(Entry)