Can you describe what you're seeing as attitude/disrespect?
What's the scenarios where this is occurring?
Towards you/dad/other family members? Teachers?
How are you addressing it at the moment and what effect does that have?
It's really hard to give advice without context, because it hugely depends.
e.g. Kids with ADHD can come across as disrespectful in different ways.
They can lack a sort of "brain to mouth filter" (impulse control) - they may then have awareness that this is inappropriate and be apologetic about it afterwards, but not be able to stop themselves in the moment. OR, if it's been ignored/accepted previously, then they may literally not understand that it's considered rude, or find it hard to break the habit. Or they may have a bit of trouble following social rules too, so find it difficult/frustrating to follow why it's fine to say something in one context but not in another. E.g. it's OK to tease someone jokingly/affectionately especially within a family, but some subjects are not OK to tease about ever. It's funny to tell a joke with the right timing, it's annoying to repeat it loudly multiple times, interrupting adult conversation. Or an aunt may call a child a "silly sausage" but if the child says that back to a teacher, it might not go down well.
They may have less awareness of volume and tone than other children their age. You could practice this and have an unobtrusive code word which communicates "tone is slipping into disrespectful" but does not mean that you are telling them off.
They may find it harder to hide their feelings such as sighing or rolling their eyes when they feel frustrated or bored. Or they may be distracted by other things in the room. Adults can interpret this as disrespect or attitude.
ADHD emotional dysregulation can cause children to react much more strongly to being told off, corrected, or asked to stop and they may "kick back" - in general it is best to ignore this otherwise it will simply escalate because the child is unlikely to be able to wind that down once it has been started. This can also activate a nervous system response where the child goes into protection mode. (If you frequently find that correcting a rude tone escalates into much more serious aggression or violence, this is probably what is happening.)
There may also be some demand avoidant tendencies, where the child instinctively kicks off in response to a perceived loss of autonomy but will basically calm down and forget about this, if you don't then escalate it by policing their tone.
ADHD executive dysfunction can cause genuine difficulty in completing tasks or expectations from adults, but the child answering honestly can come across as disrespectful, "excuses" or backtalk by adults. This is EXTREMELY common, and as an adult with ADHD, I find this one the saddest and most frustrating - because the child is trying to tell the truth, but adults misinterpret this all the time, which leads to the child developing a coping mechanism which is to lie or give the answer that they know adults want to hear such as "I'm sorry, I won't do it again" or "I will try harder next time". Then because they do not actually know how to try harder/not do it next time, they invariably repeat the same mistake and adults get more annoyed because they think the child "should" know not to do this thing. Taking child's comments at face value or most generous interpretation, then working with them to solve the problem can help enormously. Bear in mind also, that even adults often don't know why they struggle with something so children are very very unlikely to express this in a way which is clear. You have to start with curiosity as the adult and assume difficulty rather than defiance.
BTW previous paragraph also applies for children asking questions like "Why should I?" or "But I don't want to!" or "When she did it you didn't tell her off!" - the answers to these are obvious to adults and so the adults assume they are obvious to children, but the children often genuinely do not understand why it is different.
ADHD can cause scenarios where the child is being set up to fail again and again which can cause frustration. Frustration responses look very much like "attitude".
ADHD behaviour in children is also very frustrating to adults. It is not uncommon for ADHD children to hear a lot of frustrated or irritated tone from adults, or have requests accompanied by threats, particularly if the first few requests made in a more polite tone were tuned out because the ADHD child was focused on something else. Therefore, ADHD children can end up mimicking these frustrated/irritated tones from adults, and the adults find this to be rude. Not always recognising that the child is simply repeating what they commonly hear! It can help to model correcting your own tone if you catch yourself asking your child something in an irritated way, and also to get the child's attention before you make a request of them, such as going up to them and placing a hand on their shoulder.
And yes there are other causes such as underlying needs.
The child may have a sensory need e.g. for movement which is not being met.
They may be bothered by sensory input in the environment e.g. noises, smells, light fluctuation.
The child may struggle to sleep and need more sleep.
They may eat poorly or not enough and need more nutrients or simply calories. Their blood sugar might be spiking all day if they primarily eat simple carbs or highly sugary foods.
They may benefit from medication, or their medication may be causing the irritatability and need to be adjusted.
The child may have poor attention to their internal body systems and therefore not recognise when they need to wee/poo/eat/drink/adjust clothing for comfort etc but be bothered by the sensations of full bladder/colon or hunger or too hot/cold but not realise this is what is bothering them.
They may be struggling with some aspect of school e.g. friendships, or the actual school work.
They may feel that this adult does not like them. They may have a self-image as a "bad" kid, if they are frequently in trouble.