The following Pokémon GO forms cannot learn a second charged move, unless Shadow (in which case they can learn one in addition to Frustration) or Purified (in which case they can learn one in addition to Return).
TForm
bugCaterpie (*)
bugMetapod (*)
bug poisonWeedle (*)
bug poisonKakuna (*)
waterMagikarp (*)
normalDitto
psychicUnown
psychicWobbuffet (*)
normalSmeargle
bugWurmple
bugSilcoon
bugCascoon
normal flyingTaillow (*)
waterFeebas (*)
psychicWynaut
steel psychicBeldum (*)
bugKricketot
bugBurmy Plant
bugBurmy Sandy
bugBurmy Trash
bug flyingCombee
normalHappiny
electricTynamo
bugScatterbug
bugSpewpa
bug waterWimpod (*)
psychicCosmog
psychicCosmoem
bugBlipbug
grass dragonApplin
electric poisonToxel
dragon ghostDreepy
ghostGimmighoul

(*) has a Shadow/Purified form, which knows Frustration/Return
Pokémon GO: A Quantitative Approach