Why any set works
Standard TKL means standard everything: 6.25u spacebar, normal modifiers, no odd right Shift. If a keycap set exists, it almost certainly includes full TKL coverage. ISO K8 Pros need an ISO Enter and short left Shift, as with any ISO board.
Profile considerations
The K8 Pro ships with OSA-profile double-shot PBT. Any profile fits mechanically; if your unit is a hot-swap version, its sockets are south-facing on the Pro generation, so Cherry-profile interference is not a concern.
Practical upgrade path
Most owners either go shine-through for the backlight or thick PBT for sound. Since the layout is standard, sets can move with you to any future TKL, making this a safe place to spend on nicer caps.
OSA in context: what changing profile does
OSA is Keychron's house profile: roughly OEM height with spherical, lightly scooped tops. Moving to Cherry profile drops the caps lower and flatter, the common pick for sound and for typists who like a lower wrist angle. SA goes the other way, tall and heavily sculpted, and takes adjustment. Uniform profiles like XDA and DSA are flat across every row, loved by people who remap layouts and disorienting to everyone else at first. None of this affects fitment; on a standard board like the K8 Pro, profile is purely a feel and sound decision, and Cherry remains the community's low-risk default recommendation.
Reading the stock caps before you spend
The stock caps are better than the upgrade instinct assumes. Double-shot construction means each legend is a second piece of plastic that cannot wear off, and PBT resists the greasy shine that ABS develops under heavy use, so durability is rarely a real reason to replace them. The honest reasons are backlight and looks: the stock legends are not shine-through, and OSA's rounded aesthetic is distinctive rather than neutral. A quick field test if you bought the board secondhand: caps that have gone glossy where fingers rest are likely ABS replacements rather than the original PBT, and a previous owner's set may be missing sizes.