Problem has been solved 
Hello and welcome to the forum!
Getting the chart, watch, and sextant is a miniquest unto itself. You have to talk to the observatory professor with a coordinate clue in your inventory. Then talk to Murphy, Kojo, and the professor again in that order.
Good luck on the treasure hunt!
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Thank you Mod Branon
I didn’t know I had to have the clue in my inventory when talking to the professor… I was reading/watching some guides (but OSRS which is 2007-present) that didn’t mention that. It was driving me mad 
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