Prove Your Strength

Here's how I got them all in a timely manner:

Started off at Affliction Ridge (roughly 46,64) and got:

[item=114038] from [npc=83458]
[item=114023] from [npc=80689]
[item=114021] from [npc=80685]
[item=114025] from [npc=80696]
[item=113590] from [npc=80690]

I then went north to the Ogron cave entrance at 43.6 48.2 for:

[item=114019] from [npc=81240]

Back south to Mistcreep Mire (50,69) for:

[item=114034] from [npc=85695]
[item=114036] from [npc=85694]

And lastly, I ran south out of the mire into Razorbloom (48.50, 75.30) for:

[item=114027] from [npc=81617]
[item=114032] from [npc=85779]
[item=114030] from [npc=81630]

At said coordinates the 3 mobs are within 30 yards of each other. Remember that the Bloom Defender has quite a big chunk of health so it is advised to just nuke it down a bit before popping your Champion.

Of course you can also do it in a different order per group, I did it on the spot. In the end you got 10 minutes in between each time so it won't get any faster than 30-40 minutes anyhow.

To complete this guide I will also add what others have stressed, you need to pop [spell=164012] which you get from choosing The Sparring Arena. The Champion summoned fights by your side for one minute.

Hope this helps! Good luck!

Thanks to TheRealZych and mymy379 for their additions.

The required items drop from specific creature types while having an active champion.

Active champion? Use the outpost ability [spell=164221]. (Requires the Sparring Arena outpost in Gorgrond.)
During its 1 minute duration, you can gather the items. Afterwards you have to wait for the 10 minute cooldown to pass.

Upon completion you get the quest Trophy Hunter of Gorgrond / Trophy Hunter of Gorgrond which according to the text would reward something - but it doesn't seem to yet.

 Item

Creature type

Example NPC

 [item=114030]

Ancient tree

[npc=81630]

 [item=114036]

Basilisk

[npc=85694]

 [item=114025]

Botani (plant men) 

[npc=81575]

 [item=114038]

Steam elemental

[npc=81685]

 [item=113590] 

Goren

[npc=80690]

 [item=114023]

Gronn

[npc=80689]

 [item=114021]

Gronnling

[npc=80685]

 [item=114019]

Ogron

[npc=81240] (Inside cave at 43.5, 48.1) 

 [item=114027]

Infested Orc

[npc=81617]

 [item=114032]

Ravager

[npc=81561]

 [item=114034]

Wasp

[npc=85695]

Most of them seem to have a high drop chance, but some might require a few kills. (Or a lot.. depending on bad luck.)

/way Gorgrond 43.8, 81.0 Silent Watcher
/way Gorgrond 51.0, 68.8 Mire Basilisk
/way Gorgrond 43.8, 78.4 Bloom Weaver
/way Gorgrond 43.2, 62.0 Turbulent Steamfury
/way Gorgrond 43.8, 64.8 Goren Gouger
/way Gorgrond 46.6, 46.6 Canyon Boulderbreaker
/way Gorgrond 45.8, 65.6 Gronnling Bonebreaker
/way Gorgrond 43.0, 47.4 Ogron Spinecrusher
/way Gorgrond 48.2, 72.8 Infested Orc
/way Gorgrond 45.6, 80.6 Thicket Ravager
/way Gorgrond 52.6, 67.6 Mistcreep Stinger