Hello, I have a custom magic wand that I'm having trouble with. 

My first issue, I have a modifiers that give resistance to Necrotic damage and Advantage to spell attacks against the undead. But when I check over the Character Sheet in features and traits as well as the item itself it does not show that information anywhere. 

Lastly, I have the spell Dominate Monster on the item and I added the restriction that it can only target Undead creatures. Again, when I check the spell on the Character Sheet it does not have the restriction anywhere.

Is there a way for me to have these appear or do me and my players just have to remember this effects?

Thank you!

Firstly, you posted this in Feedback. You should post Homebrew questions and such in the Homebrew forum. I will request a mod move this for you. Just to let you know for future. I also recommend checking the pinned threads in that forum as they have very helpful guides, the most helpful of which is pinned in my signature below.

Quote from Badman17 >>

My first issue, I have a modifiers that give resistance to Necrotic damage and Advantage to spell attacks against the undead. But when I check over the Character Sheet in features and traits as well as the item itself it does not show that information anywhere. 

 
The resistance will be displayed in the box under the HP area on the character sheet (website) in the defenses column. This is if the modifier set up correctly.

Modifier Type: Resistance
Modifier Sub-Type: Necrotic

There is no way to display advantage to any attack on the sheet by any feature. This will only be detailed in the item description. While you can create modifiers for this - this doesn't do anything on the sheet. The player will have to remember this or make a note (on PC they can use the native Sticky Notes app or Notepad). 

Quote from Badman17 >>

Lastly, I have the spell Dominate Monster on the item and I added the restriction that it can only target Undead creatures. Again, when I check the spell on the Character Sheet it does not have the restriction anywhere.

 
There is no way to detail his restriction. 

If you don't have any intention of sharing this item to the public and it is only to be used in your campaign (noting that all homebrew created is automatically shared with everyone in the same campaign, no subscriptions or public sharing required), then you can get this working perfectly. Make a Copy of the Dominate Monster spell, rename it Dominate Undead, and change the spell description text so "monster" is replaced with "undead". Then you add this homebrewed spell to the wand. 

Quote from Cyb3rM1nd >>

Quote from Badman17 >>

My first issue, I have a modifiers that give resistance to Necrotic damage and Advantage to spell attacks against the undead. But when I check over the Character Sheet in features and traits as well as the item itself it does not show that information anywhere. 

 
The resistance will be displayed in the box under the HP area on the character sheet (website) in the defenses column. This is if the modifier set up correctly.

Modifier Type: Resistance
Modifier Sub-Type: Necrotic

There is no way to display advantage to any attack on the sheet by any feature. This will only be detailed in the item description. While you can create modifiers for this - this doesn't do anything on the sheet. The player will have to remember this or make a note (on PC they can use the native Sticky Notes app or Notepad).

 
Regarding making notes to display the advantage - here's a video I just made that shows how to make a note in your attacks section so you can easily remind yourself about advantage.