A 5k spiritual beast exp is an item in Evony TKR (The King's Return). It can be found after killing certain monsters or bosses, with some of them listed below.
The description of 5K Spiritual Beast EXP in Evony TKR says:
Use it to gain 5,000 Spiritual Beast EXP for any Spiritual Beast.
5K Spiritual Beast EXP is known to drop from a number of bosses or monsters upon killing, including Minotaur, Griffin, Senior Nian, Medium Nian, Junior Nian, Ifrit, Kamaitachi, Fafnir, Lava Turtle, Warlord, Golem, Witch, Junior Hydra, Medium Hydra, Senior Hydra, Junior Cerberus, Medium Cerberus, Senior Cerberus and Ymir.
Note: This list may be incomplete.