An eldritch knight adds his level to any levels of fighter he might have for the purpose of meeting the prerequisites for feats (if he has no fighter levels, treat his eldritch knight levels as levels of fighter). He also adds his level to any levels in an arcane spellcasting class for the purpose of meeting the prerequisites for feats.
I suppose what I'm asking is can a Fighter2/Wizard8/Eldritch Knight 10 select arcane discoveries as if he were an 18th level wizard? If not, the only feats I know of that it would 'help' qualify for are Spell Mastery(Requires 1st level Wizard), Create Sanguine Elixir(Sorc 3rd), or Split Hex(Witch 10. The only one it actually helps with, since the others are fulfilled by the time you qualify for EK)
Yes, Eldritch Knight explicitly adds to your wizard class level for the purpose of meeting the prerequisite of feats. Arcane Discoveries are basically just feats that - due to being wizard-exclusive - were listed in the wizard section of the Ultimate Magic sourcebook rather than amongst the general feats.