Hi Nick,
This was a bit of a discussion point for my husband and me, because this is not a sentence we would use on a daily basis.
But... what i think, and correct me if I am wrong, is that Jip did something bad, or said something bad.... in that case 'vader kijkt Jip eens aan' becomes like in English: Father gave Jip THE look.
Or it could also mean, depending on context, 'father looked at Jip with amazement/ confusion.
'Eens' we would use more often in a commanding form.
Kijk me eens aan.
Doe je schoenen eens aan.
Kom eens hier.
I hope this helps,
Pascale