To identify the variables used on the Email Templates and through the website, navigate to Emails - Email Templates.
The list can be found here:
Special Note Regarding Variable Names
With the following information about SEO variables set, there is another point that needs to be made regarding SEO variable names. Avoid naming a SEO variable name the same as a column on the database. For example, the following is a list of columns names found in the database that should not be used as SEO variable names:
type, old_filename, new_filename, updated_by, name, icon, keywords, order, group_name, database, first_name, last_name, email, company, phone_number, fax_number, address1, address2, zip_code, city, state_code, country_code, state_ln, country_ln, website, twitter, facebook, linkedin, blog, active, token, position, profession, additional, link, link_order, user_id, comments, data_name, data_type, form, form_name, search_results, h1, h2, post_type, widget, widget_name, status, title, section, filename, quote, experience, affiliation, awards, published, education, softwares, fees, about_me, featured, testimonial, preferred, work_experience, rep_matters, speaking_engagements, current_position, additional_fields, lat, lon, post_title, post_caption, post_category, post_image, post_price, post_tags, group_category, property_status, property_type, property_beds, property_baths, property_price
This is because they will have a conflict between each other.