There is little that can be done to change a person's self-image. However, you can organize your department to accommodate the Know-It-All and give her a chance to participate and be recognized for what she does know. If the Know-It-All is your peer, you can also play to her strengths rather than become an antagonist. To start with, don't challenge her intellectual superiority. This is especially important if the Know-It-All is your boss or someone higher. You'll just make an enemy you don't need.
Let the Know-It-All be the smartest of the smart. Graciously accept the information she shares. You never know when information, no matter how abrasive the source, might be helpful.
ENCOURAGE THE KNOW-IT-ALL TO PARTICIPATE
Go to the Know-It-All for information first. Ask for her help figuring something out. When research needs to be done, assign it to the Know-It-All, and get her involved in departmental activities that play well into her self-image. Compliment and reward her for having vital knowledge that you need. Businesses run on information. The Know-It-All is a valuable asset.
CHALLENGE THE KNOW-IT-ALL TO GO DEEPER
It's one thing to know facts and figures. If the Know-It-All is conducting research on your behalf or for the team you're on, ask how her findings can best be applied. Then put her opinion to highly visible use.
MAKE PRACTICAL ASSIGNMENTS
Putting the Know-It-All in charge of solving complex puzzles makes sense, given her strong desire to know everything. Gathering contact data for a marketing campaign that includes studying demographics, geographical release timing, product planning, and preparation will really draw on the Know-It-All's brainpower.
Give the Know-It-All team leadership responsibility for information-related activities. Choose other people who are also curious and research oriented to be part of the team. They will appreciate the Know-It-All's desire for knowledge. Make the team assignment clear. Tell them: "We need information that we can use right now to extend our competitive advantage. So-and-so here is an expert at gathering and analyzing data. All of you can participate and, together, you can turn the raw data into useful information."
SHARE YOUR KNOW-IT-ALL
Tell other department heads and your boss that, if you had a position for a Chief Knowledge Officer, your Know-It-All would have the title. It won't hurt your career ambitions or standing within the organization to be a champion of applied knowledge. Or ask the Know-It-All to join you at high-level meetings to advise on data resource issues. Instead of playing the role of "font of all information," defer to the Know-It-All. When acknowledged, she won't feel a need to convince others of the superiority of her intellect.
Ask the Know-It-All to represent you and the department at interdepartmental meetings. Tell her you have faith in her knowledge of the department. She will be able to represent the department well and answer all questions, especially the detailed questions that demand an explaination of the thinking behind decisions. Ask the Know-It-All to begin creating an information warehouse to document all of the information and resources important to your department. This plays into the Know-It-All's natural desire to be Information Central. Demand that the information warehouse be accessible to everyone who can put the data to good use.
The more you acknowledge the Know-It-All's intelligence, the less contempt she will express toward you and others. Give credit where credit is due. The more you pump up and publicize the Know-It-All's good work, the less she will want to be put in charge of everything else, too. Even with Know-It-Alls, rewarded behavior is repeated behavior.