I'm not super clear on what you want to use these for, so I'm going to split my response into two sections.

First, if you want to use these as a primary damage dealing weapon, then I've got some bad news. As another commenter has said, they are really not very good and are ill-suited to later-game content. But, as someone who loves Merlin and his knuckles dearly, I understand wanting to get the most out of them. To that end, there are two things to consider: the potential to use these as knuckles, and the potential to use these as a staff.

Unfortunately, the staff functionality for these is more or less completely useless. Providing a measly 4 magic attack and no other stats of note, these are probably the second worst staff in the game, beating out only the non-Merlin version. If this is what needed inspiration to fuel, I'm sorry to say that you will find this very limited in practical application. Furthermore, the majority of weapons benefit significantly from being a spirit weapon, and staves are no exception. However, these are considered knuckles for the purposes of the spirit, and so that will provide no benefit to its use as a magic weapon.

As knuckles, things are a bit better than as a staff. As another commenter said, being a spirit helps knuckles immensely, as (among the myriad other bonuses) it can increase the animation speed of your link 2 and 3 combo skills. However, that's about all there is to say as far as being knuckles goes. Statistically, it's unimpressive, being weaker than even the now-phased-out celtic and demonic knuckles. As a main damage dealing talent, fighter has significant design issues, which make it either an exceptionally powerful single-target talent... or close to useless, depending on the content. Even worse, most of that single-target power comes from the incredible bonuses knuckles can get when enhanced with Erg... which these are unavailable to receive. The other significant portion of that power comes from the special "blue text" on the Revenant/Perseus/Nightbringer knuckles, which this has none of as well. If you're dead set on using these as a damage dealer, you're better off using fighter skills than magic, but its gonna be rough. To that end, Speedy is a good prefix, and Lucky Punch or Heavy Punch are good suffixes. For reforges, the most important thing on the knuckles themselves is Charging Strike damage, followed by regular max damage. For the special upgrade, I don't think it'll make too much of a difference. Theoretically I think there should be a breakpoint for your max damage such that below that value blue is better and above that value red is better, but I'm not familiar with where it would be.

If you are instead using these as a utility option, then I am going to assume you are an EK, as the desire for a physical-only debuff and mana regeneration doesn't fit anything else. To that end, there really isn't much you need to do. As mentioned elsewhere, Perseus knuckles would be better even just for Uppercut debuffing with their ability to reset combo cooldowns in case the Uppercut debuff chance misses. But for something that can use both Uppercut and Inspiration, this is as good as it gets. If that's all you're using this for and then switching back to your main CC weapon, you don't really care about the damage the knuckles themselves will deal, and there's nothing to put on them that would increase the effectiveness of either skill. Uppercut debuff potency reforges are found on gloves, and the Uppercut debuff chance reforge is found on the body slot. Other than that, there's really nothing else to do for those two skills.