When do Shamans learn Fire Nova?

Rank 1 at level 12, with later ranks at 22, 32, 42, 52. Visit a class trainer in any capital.

Did Fire Nova change from Classic?

Fire Nova is new in WoW Forever and had no Classic 1.12 equivalent for Shamans.

Rank	Level	Cost / range / cast	Effect	Classic 1.12
Rank 1	12	65 Mana · 30 yd range · Instant · 10 sec cooldown	Instantly inflicts 32 to 38 fire damage to enemies within 10 yd of your active Fire totem. Coefficient 14.3% of spell power (direct)	new
Rank 2	22	120 Mana · 30 yd range · Instant · 10 sec cooldown	Instantly inflicts 54 to 62 fire damage to enemies within 10 yd of your active Fire totem. Coefficient 14.3% of spell power (direct)	new
Rank 3	32	210 Mana · 30 yd range · Instant · 10 sec cooldown	Instantly inflicts 126 to 142 fire damage to enemies within 10 yd of your active Fire totem. Coefficient 14.3% of spell power (direct)	new
Rank 4	42	290 Mana · 30 yd range · Instant · 10 sec cooldown	Instantly inflicts 173 to 195 fire damage to enemies within 10 yd of your active Fire totem. Coefficient 14.3% of spell power (direct)	new
Rank 5	52	375 Mana · 30 yd range · Instant · 10 sec cooldown	Instantly inflicts 232 to 258 fire damage to enemies within 10 yd of your active Fire totem. Coefficient 14.3% of spell power (direct)	new

Call of Flame (Elemental row 2): Increases the damage done by your Fire Totems and by your Flame Shock and Fire Nova spells by 15%, as well as increases the duration of your Flame Shock spell by 9 sec.
Trial by Fire (Elemental row 4): Increases the damage done by your Fire Nova spell by 20% and reduces its cooldown by 4 sec, and increases the duration of your Magma Totem by 20 sec.
Elemental Reach (Elemental row 5): Increases the range of your Lightning Bolt, Chain Lightning, and Fire Nova spells by 6 yards.

Source: beta client 1.60.1.70753. Spell ID 408345.