That style of knife is known as a "trench knife". Unfortunately I have strong reason to believe that your knife is a fake, possibly a Kult of Athena fake (Kult of Athena sells "reproductions"). From what I read there are a lot of fake Gottlieb Hammesfahr trench knives, typically made in India.
I was reading about these knives on a WW1 weapons forum, and here's what I've got-
The knife on the left in both sets of pictures below is said to be a genuine WW1 Gottlieb Hammesfahr trench knife, the knife on the right is your knife.
The stamps, both proof mark and text/name markings, are on opposite sides. This is said to be a common sign of a fake.
Pic of proof marks.
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The grooves across the handles are going in the opposite direction. This is said to be another sign of a fake.
The grooves on the left knife are angled back, the grooves on your knife are angled forward.
To illustrate-
left knife [///////]>>>>>>
right knife [\\\\\\\]>>>>>>
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Of course you can research such things yourself by searching the internet for "Gottlieb Hammesfahr trench knife", and "Gottlieb Hammesfahr trench knife fake". You can also look at the one pictured at "Kult of Athena" and compare it to yours.
Here's a pic of a Kult of Athena fake Gottlieb Hammesfahr. The tang stamp looks a lot like yours.
View attachment 2835448
Your knife.
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