As a DM I wouldn't allow it, because it's not using a skill like making an arcana check for knowledge, it's your magical might vs the spell's resistance.Jack of all trades specifically says "add half your proficiency to any ability check that does not already add your proficiency bonus." So, if Dispel magic does not include proficiency bonus, it is affected by Jack of all trades.
EDIT: Guidance also does apply, since it works on "Ability Checks", and dispel magic says "Make an ability check"
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