I'm getting a Marshall DSL 15C, but I also want a looper pedal, but the amp does not have an fx loop. Will a looper pedal work in front of the amp?
Yes, but you won't be able to go clean-dirty-clean without an od pedal between you guitar and looper. And if you set your amp up dirty or gainy, the sound from the looper will be the same.
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i'm sorry I dont understand. I was thinking guitar > looper> amp and still get heavy distortion from the amp? and for solos guitar>sd-1>looper> amp will that work?
if you record dirty for example, then switch to the clean channel, the tone will now be clean coming from the looper.

it'll just record the raw sound not the distorted sound from the amp.
No it won't work properly. The looper is a recorder. A recorder should be the last link in the chain. Distorted tones coming from the amp will ruin any signal coming from the looper and turn your sound into mud.
That being said... if you keep your amp clean and get your dirt from pedals before the looper then it should sound ok.