When asking questions informally, we often drop the question marker, KA, and raise the intonation at the end of the sentence so the other party knows it's a question. And when writing informally, we usually put a question mark at the end so it's clearly a question.
あした、かいものいく？(ASHITA KAIMONO IKU? = Will you go shopping tomorrow?) きょう、クラスのあと、としょかんいく？(KYOU KURASU NO ATO, TOSHOKAN IKU? = After class today, are you going to the library?)
Also, there are some popular informal endings like NO and NANO you can use instead of KA:
A: あした かのじょが にほんから くる。(ASHITA KANOJO GA NIHON KARA KURU = Tomorrow, my girlfriend is coming from Japan.) B: そうなの？(SOU NANO? = Is that so?) A: そう。だから、きょうは はやくかえって うちのそうじを しなきゃ。(SOU. DAKARA KYOU WA HAYAKU KAETTE UCHI NO SOUJI O SHINAKYA = Yes. So I have to go home early today and clean up my room.)
A: らいしゅうは、にほんごの テストが あるの？(RAISHUU WA NIHONGO NO TESUTO GA ARU NO? = Are you going to have a Japanese test next week?) B: そう、きまつテストが ある。(SOU, KIMATSU TESUTO GA ARU = Yes. I'm going to have a final test.) A: がんばってね。なんようびなの？(GANBATTE NE? NANYOUBI NANO? = Good luck. What day of the week?) B: げつようび。だから、こんしゅうの しゅうまつは、べんきょうで いそがしいよ。(GETSUYOUBI. DAKARA KONSHUU NO SHUUMATSU WA, BENKYOU DE ISOGASHII YO = Monday. So I will be busy with studying this weekend.)
NO and NANO endings are more popular among women, but they are used by men as well. NANO is covered in Course 3 Lesson 9 Grammar.
Some men tend put KA right after informal verbs and adjectives. They, however, do not put KA after informal noun endings, which is DA. Instead, they drop DA and put KA right after nouns. You have to remember, thought, women rarely do that.