single word requests - Adjective to describe someone who is knowledgeable, resolute, and calm

Particularly consider level-headed, which was briefly mentioned in two other answers:

(idiomatic) Sensible; rational; possessing sound judgment.
Usage notes: Often having the connotation of remaining calm, composed, and careful, of not acting out of reflex or excessive emotion.
Synonyms: calm,
deliberative, stable

Several phrases or hyphenated compounds starting with even may apply:
• on an even keel (or, even-keeled), “(idiomatic, of emotions, etc.) The state or characteristic of being under control and balanced.” and “(idiomatic, of a business or other activity) The state or characteristic of being well controlled and running smoothly.”
• even-tempered, “Remaining calm even in situations that would cause many others to become angry, frustrated, panicky, etc.”
• even-minded, “Having equanimity” [which is, “the state of being calm, stable and composed, especially under stress”]
• even-handed, “Treating fairly.”

Here are a few more words to consider as well, of varying relevance depending on the circumstances you want to describe. (Some may go a bit far afield.)

• sedulous, “Diligent in application or pursuit; constant, steady, and persevering in business or in endeavors to effect an object; steadily industrious; assiduous.”
• assiduous, “Hard-working, diligent or regular (in attendance or work); industrious.”
• perseverant, “Enduring; persistent.” (Someone who keeps on trucking, come what may, is perseverant.)
• determined, “Decided; resolute, possessing much determination.”
• resolute, “Firm, unyielding, determined.”
• intrepid, “Fearless; bold; brave.”
• tenacious, with the sense “unwilling to yield or give up; dogged” perhaps being most well-known, but the sense “holding together; cohesive” may be more relevant in the context of the question.
• fortitudinous, “Having fortitude; courageous”
• impartial, “Treating all parties, rivals, or disputants equally; not partial; not biased; fair.”
• stoical, “Enduring pain and hardship without showing feeling or complaint.”
• valiant, “Showing courage or determination; heroic.”
• stalwart, “Firmly built” or “Courageous”.
Synonyms of of stalwart under the two senses include, for the firmly built sense, firm, resilient, stout, strong, robust; and for the courageous sense, brave, bold, courageous, daring, valiant.

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