Finding the major contributing tautomer of 1-(propan-2-yl)-1,2,3,5-tetrahydro-6H-pyrazolo[3,4-b]pyridin-6-one
In keto-enol tautomerism, the equilibrium is mostly towards the keto form, as it should be, since $\ce{C=O}$ is a very strong and stable bond. In some cases however we find that the equilibrium sometimes shifts to enol form. This happens in cases where some additional benefit is done by the enol structure. here are two examples:
A) Removing anti-aromaticity or adding aromaticity to a ring.
B) Extended conjugation formation, providing additional stability.
In the structure you have shown, the enol form is more stable because it adds aromatic character to the ring. This additional stability drives the equilibrium
towards the enol form.