を問わず means "regardless of," "irrespective of," or "no matter." It is used to express that something applies universally, without being affected by a particular condition or distinction. The literal meaning comes from the verb とう問う (to question/to ask) in its negative form – "without questioning."
Attach を問わず directly to a noun to indicate that the outcome or statement holds true regardless of that noun.
を問わず is very common with pairs of contrasting options – similar to "whether A or B." These pairs are often written without a particle between them.
You can also use を問わず after a clause ending in かどうか to mean "regardless of whether or not."
を問わず is relatively formal and is frequently found in written language such as job postings, official announcements, rules, and news articles. In casual conversation, expressions like 〜~にかんけいなく関係なく or 〜~にかかわらず may be used instead, though 〜~にかかわらず is also fairly formal. を問わず tends to attach to broad categorical nouns (age, gender, nationality, experience, etc.) rather than specific or concrete items.