When do Priests learn Penance?

Rank 1 at level 30, with later ranks at 40, 50, 60. Visit a class trainer in any capital.

Did Penance change from Classic?

Penance is new in WoW Forever and had no Classic 1.12 equivalent for Priests.

Rank	Level	Cost / range / cast	Effect	Classic 1.12
Rank 1	30	Enemy: 36 yd range · 150 Mana · Friendly: 40 yd range · Channeled · 12 sec cooldown	Launches a volley of holy light at the target, causing 44 Holy damage to an enemy, or 133 healing to an ally, instantly and every 1 sec for 2 sec. Coefficient 19% of spell power (heal), 19% of spell power (per tick)	new
Rank 2	40	Enemy: 36 yd range · 220 Mana · Friendly: 40 yd range · Channeled · 12 sec cooldown	Launches a volley of holy light at the target, causing 52 Holy damage to an enemy, or 208 healing to an ally, instantly and every 1 sec for 2 sec. Coefficient 19% of spell power (heal), 19% of spell power (per tick)	new
Rank 3	50	Enemy: 36 yd range · 270 Mana · Friendly: 40 yd range · Channeled · 12 sec cooldown	Launches a volley of holy light at the target, causing 71 Holy damage to an enemy, or 279 healing to an ally, instantly and every 1 sec for 2 sec. Coefficient 19% of spell power (heal), 19% of spell power (per tick)	new
Rank 4	60	Enemy: 36 yd range · 385 Mana · Friendly: 40 yd range · Channeled · 12 sec cooldown	Launches a volley of holy light at the target, causing 92 Holy damage to an enemy, or 425 healing to an ally, instantly and every 1 sec for 2 sec. Coefficient 19% of spell power (heal), 19% of spell power (per tick)	new

Power in Light (Discipline row 1): Your Smite and Penance spells deal 10% increased damage to targets afflicted with your Holy Fire or Shadow Word: Pain.
Penance (Discipline row 5): Launches a volley of holy light at the target, causing 44 Holy damage to an enemy, or 133 healing to an ally, instantly and every 1 sec for 2 sec.
Renewed Hope (Discipline row 5): Your heals from Flash Heal, Lesser Heal, Heal, Greater Heal, and Penance gain 10% increased critical strike chance when cast on targets with Weakened Soul, and reduce the remaining duration of Weakened Soul on their target by 5 sec.
Improved Healing (Holy row 4): Reduces the Mana cost of your Lesser Heal, Heal, Greater Heal, Penance, and Prayer of Mending spells by 15%.

Source: beta client 1.60.1.70753. Spell ID 1316995.