Looks like, from here, a 3.5mm jack socket, or a barrel-jack, something like...

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But without measuring kinda guessing.

You'd use EITHER that or add another 2-pin connector to the Probe inputs, then take the wires to the probe.

EDIT:

Okay, just read your reply - yeah, it could be a good idea to eat some holes into the case and mount some appropriate chassis connectors, then route these back to this board.