[Cola]

Hi. I'm not a native speaker, but I believe most people say テーブル, not
たくし. In fact, this is the first time I've heard the word たくし - Microsoft IME doesn't even generate the kanji for it (卓子) automatically. Anyway, searching on Google with quotes and using kanji, 卵円のテーブル (らんえんのテーブル) produces no results, 卵形のテーブル (らんけいのテーブル) produces 22,300 results, and 楕円形のテーブル (だえんけいのテーブル) produces 173,000 results. I'd go with だえんけい for oval.

Also, do you mean, "Is the table oval?" or "What is an oval table?"? What you wrote in Japanese is close to "Is the table oval?"

"What is an oval table?" would be "だえんけいのテーブルはなんですか？"

"Is the table oval?" would be "テーブルはだえんけいですか？"

Also, there is no word for "an" or "the" in Japanese. There are grammar constructions that serve similar functions, but, needless to say, they are used very differently.