Asking “what are you doing”

[gilded sparrow]

I use pleco to help me study but I’m unsure how exactly to tell differences and tones attitude and situation wise. Some words come up as casual and formal others just casual meanings. I’m not sure if I’m explaining it right but it’s confusing me on when to use certain characters/words when.
Do all of these have different meanings or tones like attitude

I was watching a tv show and it sounded like 你干什么
But was pronounced (nee-ga-sha-ma) when pinyin reads (nǐ gàn shénme)
Im assuming all languages like Chinese naturally also slur sounds together like English?
For this example leaving out the ‘n’ sound

I do realize they are saying in pinyin (ni gan shenme) Usually as a “ what the heck are you doing” kind of tone. Is this the most common way to say it or is that phrase only used in situations like that?
What’s a more casual polite way to ask what someone is up to?

[rugged kestrel]

I always say 你在幹嘛？

[frigid tangle]

什么 is generally pronounced she2me or she3me, might get reduced further to 啥 sha2

[solar shore]

在干什么呢？
在干嘛呢？
在干啥呢？ (northern)
Avoiding 你 would make the sentence softer.
Adding a 呢 at the end would do, too.